gitignore: clean up
gitignore: clean up

This removes several outdated or unnecessary ignore patterns.
Especially those that match random words such as 'local' or 'core',
which repeatedly caused weird behavior that's hard to debug, e.g.
invisble vendored files.

tomwilkie/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,datajet-io/prometheus,Stackdriver/stackdriver-prometheus,adamron1/prometheus,JavierZunzunegui/prometheus,alileza/prometheus,adamron1/prometheus,GoogleCloudPlatform/prometheus,agaoglu/prometheus,agaoglu/prometheus,kzittritsch/prometheus,kangwoo/prometheus,PrFalken/prometheus,GoogleCloudPlatform/prometheus,PrFalken/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,amorken/prometheus,brancz/prometheus,kzittritsch/prometheus,amorken/prometheus,prometheus/prometheus,tattsun/prometheus,brancz/prometheus,kzittritsch/prometheus,slok/prometheus,PrFalken/prometheus,tattsun/prometheus,AlekSi/prometheus,dsymonds/prometheus,kangwoo/prometheus,Colstuwjx/prometheus,AlekSi/prometheus,slok/prometheus,alileza/prometheus,Colstuwjx/prometheus,SaltedMan/prometheus-annotated,tomwilkie/prometheus,PrFalken/prometheus,dsymonds/prometheus,Stackdriver/stackdriver-prometheus,ton31337/prometheus,gottwald/prometheus,dmilstein/prometheus,Stackdriver/stackdriver-prometheus,SaltedMan/prometheus-annotated,brancz/prometheus,prometheus/prometheus,tomwilkie/prometheus,SaltedMan/prometheus-annotated,dmilstein/prometheus,Gouthamve/prometheus,prometheus/prometheus,keegancsmith/prometheus,tattsun/prometheus,sudhi-vm/prometheus,SaltedMan/prometheus-annotated,amorken/prometheus,kzittritsch/prometheus,gottwald/prometheus,prometheus/prometheus,ton31337/prometheus,gottwald/prometheus,adamron1/prometheus,Colstuwjx/prometheus,keegancsmith/prometheus,kangwoo/prometheus,yanghongkjxy/prometheus,adamron1/prometheus,alileza/prometheus,keegancsmith/prometheus,brancz/prometheus,prometheus/prometheus,keegancsmith/prometheus,ton31337/prometheus,AlekSi/prometheus,Gouthamve/prometheus,dmilstein/prometheus,JavierZunzunegui/prometheus,Gouthamve/prometheus,Colstuwjx/prometheus,kangwoo/prometheus,ton31337/prometheus,msiebuhr/prometheus,Conorbro/prometheus,Conorbro/prometheus,msiebuhr/prometheus,yanghongkjxy/prometheus,alileza/prometheus,AlekSi/prometheus,datajet-io/prometheus,datajet-io/prometheus,dsymonds/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,JavierZunzunegui/prometheus,dsymonds/prometheus,Stackdriver/stackdriver-prometheus,msiebuhr/prometheus,yanghongkjxy/prometheus,Conorbro/prometheus,tomwilkie/prometheus,sudhi-vm/prometheus,datajet-io/prometheus,Gouthamve/prometheus,amorken/prometheus,agaoglu/prometheus,sudhi-vm/prometheus,dmilstein/prometheus,yanghongkjxy/prometheus,slok/prometheus,Conorbro/prometheus,slok/prometheus,GoogleCloudPlatform/prometheus,sudhi-vm/prometheus,msiebuhr/prometheus,agaoglu/prometheus,tattsun/prometheus