t/Makefile: stop setting GIT_CONFIG
Once upon a time, the setting of GIT_CONFIG in the
environment could affect how tests ran. Commit
9c3796f (Fix
setting config variables with an alternative GIT_CONFIG,
2006-06-20) unconditionally set GIT_CONFIG in the Makefile
when running tests to give us a known starting point.
This is insufficient for running the tests outside of the
Makefile, however, and
8565d2d (Make tests independent of
global config files, 2007-02-15) later set GIT_CONFIG
directly in test-lib.sh. At that point the Makefile setting
was redundant, but we never removed it. Let's do so now.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>