tests: drop unused //tests:scripts dep from the system suites

Nothing imports tests.scripts. Every use spawns a script through a path
built from repo_path(), which is Path(__file__).resolve()-based and so
lands in the git checkout, not in a runfiles tree. The suites also run as
plain pytest via tests/run_tests.sh, never as Bazel tests, so no runfiles
tree is built for them at all. The dep therefore provides nothing.

Change-Id: I2da744081cd0fc495a08524178062392fd88d2f4