Replace metaclass with __init_subclass__
Replace metaclass with __init_subclass__

saimn/astropy,saimn/astropy,pllim/astropy,lpsinger/astropy,saimn/astropy,lpsinger/astropy,saimn/astropy,lpsinger/astropy,mhvk/astropy,mhvk/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,mhvk/astropy,StuartLittlefair/astropy,astropy/astropy,larrybradley/astropy,StuartLittlefair/astropy,larrybradley/astropy,mhvk/astropy,pllim/astropy,larrybradley/astropy,lpsinger/astropy,pllim/astropy,lpsinger/astropy,astropy/astropy,astropy/astropy,larrybradley/astropy,pllim/astropy,larrybradley/astropy,saimn/astropy,astropy/astropy,pllim/astropy,StuartLittlefair/astropy,astropy/astropy,mhvk/astropy