Remove the auto-generated asm_support_gen.h

Still generate the file, just don't commit it in the repository.

The build system decides the location, which is: out/soong/.intermediates/art/tools/
cpp-define-generator/cpp-define-generator-asm-support/<arch>/gen/asm_support_gen.h

Test: test-art-host-gtest
Change-Id: I586bad682818acb5293919b84c02738bba3073ea