Move perform_clip to private method
Move perform_clip to private method

pllim/astropy,astropy/astropy,AustereCuriosity/astropy,StuartLittlefair/astropy,astropy/astropy,DougBurke/astropy,mhvk/astropy,larrybradley/astropy,mhvk/astropy,saimn/astropy,funbaker/astropy,kelle/astropy,DougBurke/astropy,funbaker/astropy,astropy/astropy,larrybradley/astropy,bsipocz/astropy,pllim/astropy,dhomeier/astropy,AustereCuriosity/astropy,saimn/astropy,StuartLittlefair/astropy,DougBurke/astropy,lpsinger/astropy,lpsinger/astropy,DougBurke/astropy,kelle/astropy,MSeifert04/astropy,astropy/astropy,funbaker/astropy,AustereCuriosity/astropy,lpsinger/astropy,kelle/astropy,mhvk/astropy,aleksandr-bakanov/astropy,pllim/astropy,lpsinger/astropy,saimn/astropy,larrybradley/astropy,StuartLittlefair/astropy,astropy/astropy,stargaser/astropy,AustereCuriosity/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,dhomeier/astropy,mhvk/astropy,stargaser/astropy,lpsinger/astropy,dhomeier/astropy,dhomeier/astropy,MSeifert04/astropy,kelle/astropy,bsipocz/astropy,bsipocz/astropy,pllim/astropy,AustereCuriosity/astropy,saimn/astropy,aleksandr-bakanov/astropy,aleksandr-bakanov/astropy,bsipocz/astropy,stargaser/astropy,StuartLittlefair/astropy,funbaker/astropy,kelle/astropy,StuartLittlefair/astropy,dhomeier/astropy,larrybradley/astropy,pllim/astropy,mhvk/astropy,saimn/astropy,MSeifert04/astropy,stargaser/astropy,MSeifert04/astropy