Table: remove support for masked arrays in structhelper.
Table: remove support for masked arrays in structhelper.

For the time being clean up structhelper to only support
regular numpy arrays.  Also replace "sta" with "table" for
clarity (at least for TLA).

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