Remove symlink to the build.ninja

From the previous change, build.ninja is generated as a symlink of
build.<product>.ninja for any missing use case of build.ninja. As this
was a temporary solution while introducing new changes, removing this
feature and move all build.ninja usage into build.<product>.ninja.

Bug: 277029044
Test: aosp_cf build succeeded
Change-Id: I6e8d2840491654fa4253b1febfaecf0ee9455a2d