removal of mock.py not reflected in packaging branch, causes builds to fail

https://code.launchpad.net/~checkbox-dev/+archive/ubuntu/ppa/+recipebuild/1465853

Building recipe:
# git-build-recipe format 0.4 deb-version {debupstream}+git{revtime}+pkg{revno:packaging}
lp:checkbox-support master
nest-part packaging lp:~checkbox-dev/checkbox-support/+git/packaging debian debian

RUN ['git-build-recipe', '--safe', '--no-build', '--manifest', '/home/buildd/build-RECIPEBRANCHBUILD-1465853/chroot-autobuild/home/buildd/work/tree/manifest', '--distribution', 'artful', '--allow-fallback-to-native', '--append-version', '~ubuntu17.10.1', '/home/buildd/build-RECIPEBRANCHBUILD-1465853/chroot-autobuild/home/buildd/work/recipe', '/home/buildd/build-RECIPEBRANCHBUILD-1465853/chroot-autobuild/home/buildd/work/tree']
Applying patch /home/buildd/build-RECIPEBRANCHBUILD-1465853/chroot-autobuild/home/buildd/work/tree/recipe/debian/patches/unvendorize
can't find file to patch at input line 21
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|From 252d8e6529b9cdbb9d64db4b91517b45c89f1a49 Mon Sep 17 00:00:00 2001
|From: Zygmunt Krynicki <email address hidden>
|Date: Thu, 8 Oct 2015 08:38:43 -0700
|Subject: Remove vendorized modules
|
|This patch replaces checkbox_support.vendor.mock with equivalent imports from
|the standard python3.3 library. Upstream will stop shipping those vendorized
|modules when support for python3.2 is no longer required.
|Upstream: not-needed
|Last-Update: 2014-04-07
|
|Patch-Name: unvendorize
|---
| checkbox_support/vendor/mock.py | 2398 +--------------------------------------
| 1 file changed, 29 insertions(+), 2369 deletions(-)
|
|diff --git a/checkbox_support/vendor/mock.py b/checkbox_support/vendor/mock.py
|index ca77df6..bd867c5 100644
|--- a/checkbox_support/vendor/mock.py
|+++ b/checkbox_support/vendor/mock.py
--------------------------
No file to patch. Skipping patch.
1 out of 1 hunk ignored
Patch /home/buildd/build-RECIPEBRANCHBUILD-1465853/chroot-autobuild/home/buildd/work/tree/recipe/debian/patches/unvendorize does not apply (enforce with -f)
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/main.py", line 164, in main
    package_version.upstream_version, working_basedir)
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/deb_util.py", line 86, in extract_upstream_tarball
    raise NoSuchTag(tag_names[0])
gitbuildrecipe.deb_util.NoSuchTag

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/deb_util.py", line 215, in convert_3_0_quilt_to_native
    ["quilt", "push", "-a", "-v"], cwd=path, env=env)
  File "/usr/lib/python3.5/subprocess.py", line 581, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['quilt', 'push', '-a', '-v']' returned non-zero exit status 1

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/bin/git-build-recipe", line 9, in <module>
    load_entry_point('git-build-recipe==0.1', 'console_scripts', 'git-build-recipe')()
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/main.py", line 172, in main
    force_native_format(working_directory, current_format)
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/deb_util.py", line 236, in force_native_format
    convert_3_0_quilt_to_native(working_tree_path)
  File "/usr/lib/python3/dist-packages/gitbuildrecipe/deb_util.py", line 223, in convert_3_0_quilt_to_native
    raise Exception("Failed to apply quilt patches")
Exception: Failed to apply quilt patches
resource.struct_rusage(ru_utime=0.764, ru_stime=0.22399999999999998, ru_maxrss=29452, ru_ixrss=0, ru_idrss=0, ru_isrss=0, ru_minflt=56466, ru_majflt=43, ru_nswap=0, ru_inblock=12984, ru_oublock=22752, ru_msgsnd=0, ru_msgrcv=0, ru_nsignals=0, ru_nvcsw=1810, ru_nivcsw=435)
RUN: /usr/share/launchpad-buildd/slavebin/in-target scan-for-processes --backend=chroot --series=artful --arch=amd64 RECIPEBRANCHBUILD-1465853
Scanning for processes to kill in build RECIPEBRANCHBUILD-1465853
RUN: /usr/share/launchpad-buildd/slavebin/in-target umount-chroot --backend=chroot --series=artful --arch=amd64 RECIPEBRANCHBUILD-1465853
Stopping target for build RECIPEBRANCHBUILD-1465853
RUN: /usr/share/launchpad-buildd/slavebin/in-target remove-build --backend=chroot --series=artful --arch=amd64 RECIPEBRANCHBUILD-1465853
Removing build RECIPEBRANCHBUILD-1465853

this seems to be because unvendorize in the packaging branch tries to patch checkbox_support/vendors/mock.py which was recently deleted in the main checkbox-support tree.