Remove accidentally tracked tests/snapshots/META-INF/main.kotlin_module

This binary kotlinc per-module metadata file was incidentally committed
in #842 ('Remove LSIF graph format support'), unrelated to that PR's
intent. It is not referenced by any build/test config and is
regenerated on every Kotlin compile by LibrarySnapshotSuite.

The matching .gitignore entry 'tests/snapshots/META-INF/' is already
in place (added in #841) but had no effect because the file was
already tracked.

Author: jupblb