13.2R/signatures: improve specificity

Improve upon recent 2bec8ac80b for release candidate 3, where I
commented out a line but overlooked the presence of:

:localBranchName:

Manual edition of the 'title: ' line, specific to release candidate 4
at the time of writing. Need to edit again when RELEASE time comes.

Approved by: gjb
Differential revision: https://reviews.freebsd.org/D39237