Uninstall homebrew packages that affect the Python build

The big-sur Kokoro builder installs Homebrew's python@3.9 package,
which broke these extension modules:

 * The _lzma module has an x86_64 slice that depends on
   /usr/local/opt/xz/lib/liblzma.5.dylib and an arm64 slice that has no
   liblzma dependency. It is loadable on x86_64 but not arm64 (missing
   _lzma_alone_decoder). This module shouldn't be distributed with our
   Python build, because while the macOS SDK has liblzma.5.tbd and
   liblzma.tbd, it has no lzma.h.

 * The _dbm module has an x86_64 slice that depends on
   /usr/local/opt/gdbm/lib/libgdbm_compat.4.dylib. It is loadable on
   arm64 but not x86_64 (missing libgdbm_compat.4.dylib). It should
   have no dependency on a libgdbm_compat dylib.

 * The _gdbm module has an x86_64 slice that depends on
   /usr/local/opt/gdbm/lib/libgdbm.6.dylib. It isn't loadable on either
   x86_64 (missing libgdbm.6.dylib) or arm64 (missing _gdbm_close).
   This module shouldn't be distributed with our Python build.

Test: manual
Change-Id: I0bc7dfefca26a08adad85a0492d5bc2cb756cfc9
1 file changed