tests: cleanup binary test vector files

tests: cleanup binary test vector files

The test4012.png test vector file that was originally used for t4012 to
check operations on binary files was later reused in other tests, making
it no longer consistent to name it after a specific test. Rename it to more
generic "test-binary-1.png".

While at it, rename test9200b to "test-binary-2.png" (even though it is
only used by t9200).

Signed-off-by: Vitaliy Ivanov <vitalivanov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>