Remove deprecated HTTP/2 metrics
Remove deprecated HTTP/2 metrics

Remove `proxy.process.http2.current_client_sessions` which is deprecated
in favour of renaming it `proxy.process.http2.current_client_connections`.

duke8253/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,vmamidi/trafficserver,dyrock/trafficserver,chitianhao/trafficserver,duke8253/trafficserver,dyrock/trafficserver,pbchou/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,davidbz/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,vmamidi/trafficserver,bryancall/trafficserver,pbchou/trafficserver,bryancall/trafficserver,davidbz/trafficserver,pbchou/trafficserver,chitianhao/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,davidbz/trafficserver,dyrock/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,dyrock/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,dyrock/trafficserver,davidbz/trafficserver,dyrock/trafficserver,bryancall/trafficserver,davidbz/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver