Remove the reference to 'Branch'

Remove the sentence "Update 'Branch' in this file if necessary."
The 'Branch' field was removed in
commit b28464e00b5bb47fd3b6b7037a0e143111f71e3d.

Replace it with
"Update 'Version' and 'CPEPrefix' in this file if necessary."

Change-Id: Id419ebc11b11e4f106e0265bb4768730966c9c58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3788661
Reviewed-by: James Zern <jzern@google.com>
Commit-Queue: James Zern <jzern@google.com>
Cr-Commit-Position: refs/heads/main@{#1028523}