t: remove unexpected SANITIZE_LEAK variables
As of 1fc7ddf3 (test-lib: unconditionally enable leak checking, 2024-11-20) we've deprecated both the GIT_TEST_PASSING_SANITIZE_LEAK
and TEST_PASSES_SANITIZE_LEAK
variables. However, some newly added tests include them by mistake. Let's clean this up.
Edited by Karthik Nayak