cmQtAutoMocUic: Remove now-unnecessary mutex around CollapseFullPath

KWSys's `CollapseFullPath` no longer maintains global state. The mutual
exclusion added by commit 51676cf655 (Autogen: Split JobEvalCacheT job
into separate moc and uic jobs, 2019-09-12, v3.16.0-rc1~94^2~7) and
commit 53d523f2e1 (autogen: fix race in depfile parsing, 2021-04-15,
v3.20.2~10^2) is no longer needed.
1 file changed