This function already calls a finishToSerial(), which waits only for the
last submission in which the buffer was used to finish.  There is no
need to call finish() beforehands.

Bug: angleproject:3213
Change-Id: I410adb80a630ff9a1cba8f7202cf002a7ea5f87b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1731551Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>