t: avoid "whitelist"

t: avoid "whitelist"

The word "whitelist" has cultural implications that are not inclusive.
Thankfully, it is not difficult to reword and avoid its use.

Focus on changes in the test scripts, since most of the changes are in
comments and test names. The renamed test_allow_var helper is only used
once inside the widely-used test_proto helper.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>