Remove check with hardcoded GERRIT_NEXT_VERSION

Checking against a fixed GERRIT_NEXT_VERSION is
a very short-sighted approach, as the next version is
evolving continuously.

Fix the issue where a stable next version was
incorrectly detected as master, just because the
Gerrit versions moved on.

Bug: Issue 11264
Change-Id: I3c3c0fd5e485ec53a5cbd21ae76154a558f2bd9f