zshrc: don't complete unavailable derived metrics
zshrc: don't complete unavailable derived metrics

Filter out global derived metrics which may not be available.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp