[blinkpy] Remove unnecessary `append_to_end_of_file` argument

This argument only exists to raise an error when it doesn't match the
`lineno` argument. This no-op change makes such an invalid state
unrepresentable.

Bug: 1149035
Change-Id: Ia904ed433fe08c867a00165302ce2d9103906ae3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4559647


Auto-Submit: Jonathan Lee <jonathanjlee@google.com>
Reviewed-by: Weizhong Xia <weizhong@google.com>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#1149373}