revert addition of --skip-soong-test flag

aosp/2045666 attempted to permit passing the `--skip-soong-tests` flag
through the `b` command to `soong_ui`, but it has been causing problems.

Test: b build '...' --skip-soong-tests is not recognized
Test: build/bazel/ci/bp2build.sh
Change-Id: I02487841d8081218dc941cb04bfa1a9e148ab6af