Code review comment for ~dirk.zimoch/epics-base:FixShellCommands

Apropos epicsEnvSet: I have got requests for a method to remove environment variables. At the moment that is not possible, but would be useful for some scripts. Currently one can only set environment variables to an empty string, but that does not trigger the default value is $(variable=default) expansions.
I propose to use epicsEnvSet with a missing value argument to delete the variable, but I have to check if it possible for all architectures. Some have unsetenv(), some support setenv("variable") without "=value". In vxWorks 5 I had to use a hack (destroy the name by setting the first char to 0).

Should I add that feature here or make a new pull request?