DPWA: add --delete-in-place to test script

Add --delete-in-place argument to
chrome/test/webapps/generate_framework_tests_and_coverage.py to allow
deleting unneeded tests in place instead of printing to stdout and ask
users to manually delete them.

Change-Id: I1c92bec0a1bd401b197d0ee763f3aaf8708cd614
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3859294


Commit-Queue: Phillis Tang <phillis@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1045908}