PGO: Remove profraw files from device after pulling to local

The generated profraw files on the device are named like
child_pool-[0-3].profraw. Typically, 1 to 4 such files are randomly
generated per run.

The script pulls the generated profraw files from the device once per
benchmark, but the profraw files on the device are not removed after
being pulled. This means the next benchmark run has a high possibility
of pulling duplicate profraw files that were generated in the previous
run.

This change removes the profraw files from the device once they are
pulled to the local machine.

BUG=411331786
TEST=Run generate_profile.py with a public benchmark, and
check that the pulled profraw files have no duplicates.

Change-Id: I47bb4464937ae6a2e83b67558777d9f360eb3d6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6467347
Reviewed-by: Wenbin Zhang <wenbinzhang@google.com>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Auto-Submit: Darren Wu <darrenwu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450570}