Always use the -f flag with rm in roll_aosp.sh
Always use the -f flag with rm in roll_aosp.sh

rm will error when the file is missing without the -f flag. We delete a
few files without checking that they exist first.

Bug: b/150458033
Change-Id: I5a104d383f59d418eaa55534526194f626c88f57
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2523372
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle