Remove malloc() from read_view_create_low()

read_view_create_low() is called on every transaction start and allocates memory for the read view created in read_view_open_now().

The problem is that the heap for that allocation is emptied on each commit and thus read view memory is reallocated on the next transaction. Memory profiling shows that memory allocated by read_view_create_low() amount to almost 100% of all allocations made by InnoDB in sysbench read-only tests.