Use RemoveInvoke in several StringTests (#37417)
Use RemoveInvoke in several StringTests (#37417)

Every test that modifies CurrentCulture should be run out-of-process (to avoid one test interfering with another, either due to leaving a thread configured inappropriately or due to platforms where changing culture actually has global impact).  A few snuck in to StringTests that weren't, and we've seen sporadic failures as a result.
ericstj/corefx,ericstj/corefx,wtgodbe/corefx,wtgodbe/corefx,wtgodbe/corefx,ViktorHofer/corefx,ViktorHofer/corefx,ViktorHofer/corefx,shimingsg/corefx,ViktorHofer/corefx,shimingsg/corefx,ViktorHofer/corefx,wtgodbe/corefx,wtgodbe/corefx,ViktorHofer/corefx,ericstj/corefx,BrennanConroy/corefx,wtgodbe/corefx,shimingsg/corefx,ericstj/corefx,ViktorHofer/corefx,shimingsg/corefx,ericstj/corefx,shimingsg/corefx,BrennanConroy/corefx,shimingsg/corefx,wtgodbe/corefx,BrennanConroy/corefx,ericstj/corefx,shimingsg/corefx,ericstj/corefx