Remove not implemented functions from get_astrom
Remove not implemented functions from get_astrom

lpsinger/astropy,StuartLittlefair/astropy,aleksandr-bakanov/astropy,mhvk/astropy,pllim/astropy,StuartLittlefair/astropy,lpsinger/astropy,pllim/astropy,saimn/astropy,dhomeier/astropy,mhvk/astropy,dhomeier/astropy,astropy/astropy,mhvk/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,dhomeier/astropy,pllim/astropy,pllim/astropy,astropy/astropy,mhvk/astropy,larrybradley/astropy,StuartLittlefair/astropy,saimn/astropy,larrybradley/astropy,astropy/astropy,aleksandr-bakanov/astropy,pllim/astropy,saimn/astropy,astropy/astropy,lpsinger/astropy,lpsinger/astropy,mhvk/astropy,aleksandr-bakanov/astropy,StuartLittlefair/astropy,astropy/astropy,dhomeier/astropy,larrybradley/astropy,lpsinger/astropy,saimn/astropy,StuartLittlefair/astropy,larrybradley/astropy,saimn/astropy,dhomeier/astropy