cvsserver: remove unused escapeRefName function

cvsserver: remove unused escapeRefName function

Function 'escapeRefName' introduced in 51a7e6dbc9 has never been used.

Despite being dead code, changes in Perl 5.41.4 exposed precedence
warning within its logic, which then caused test failures in t9402 by
logging the warnings to stderr while parsing the code. The affected
tests are t9402.30, t9402.31, t9402.32 and t9402.34.

Remove this unused function to simplify the codebase and stop the
warnings and test failures. Its corresponding unescapeRefName function,
which remains in use, has had its comments updated.

Reported-by: Jitka Plesnikova <jplesnik@redhat.com>
Signed-off-by: Ondřej Pohořelský <opohorel@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>