retrace: Fix assumption in get_min_reqs Only try to remove implied extension if it is present. Test: retrace_restricted_traces.py get_min_reqs --traces riptide_gp2 Bug: b/384714388 Change-Id: Ic0240c387012923e1918fccd2ea6c341d9a84609 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6101167 Reviewed-by: Roman Lavrov <romanl@google.com> Commit-Queue: Mark Łobodziński <mark@lunarg.com>