Remove _PAGE_CONTENT_TYPES cache.
Remove _PAGE_CONTENT_TYPES cache.

No code within Wagtail uses get_page_types now, and it doesn't really matter if external code becomes infinitessimally slower...

quru/wagtail,inonit/wagtail,mixxorz/wagtail,quru/wagtail,nealtodd/wagtail,nutztherookie/wagtail,kurtrwall/wagtail,FlipperPA/wagtail,kurtrwall/wagtail,inonit/wagtail,serzans/wagtail,nutztherookie/wagtail,gogobook/wagtail,kaedroho/wagtail,rsalmaso/wagtail,nimasmi/wagtail,iansprice/wagtail,zerolab/wagtail,FlipperPA/wagtail,gasman/wagtail,takeflight/wagtail,zerolab/wagtail,kaedroho/wagtail,zerolab/wagtail,gasman/wagtail,mixxorz/wagtail,rsalmaso/wagtail,wagtail/wagtail,davecranwell/wagtail,takeflight/wagtail,torchbox/wagtail,gogobook/wagtail,serzans/wagtail,gasman/wagtail,nealtodd/wagtail,kurtw/wagtail,chrxr/wagtail,kaedroho/wagtail,chrxr/wagtail,nutztherookie/wagtail,kurtw/wagtail,nimasmi/wagtail,mixxorz/wagtail,kaedroho/wagtail,FlipperPA/wagtail,thenewguy/wagtail,quru/wagtail,hamsterbacke23/wagtail,rsalmaso/wagtail,nealtodd/wagtail,hamsterbacke23/wagtail,thenewguy/wagtail,timorieber/wagtail,mikedingjan/wagtail,nilnvoid/wagtail,davecranwell/wagtail,JoshBarr/wagtail,zerolab/wagtail,nilnvoid/wagtail,gogobook/wagtail,nealtodd/wagtail,Toshakins/wagtail,rsalmaso/wagtail,gogobook/wagtail,hamsterbacke23/wagtail,thenewguy/wagtail,timorieber/wagtail,quru/wagtail,nilnvoid/wagtail,wagtail/wagtail,davecranwell/wagtail,Toshakins/wagtail,hamsterbacke23/wagtail,serzans/wagtail,wagtail/wagtail,takeflight/wagtail,chrxr/wagtail,timorieber/wagtail,iansprice/wagtail,serzans/wagtail,torchbox/wagtail,davecranwell/wagtail,iansprice/wagtail,nimasmi/wagtail,kurtrwall/wagtail,kaedroho/wagtail,kurtw/wagtail,jnns/wagtail,wagtail/wagtail,gasman/wagtail,JoshBarr/wagtail,Toshakins/wagtail,takeflight/wagtail,rsalmaso/wagtail,nutztherookie/wagtail,JoshBarr/wagtail,mixxorz/wagtail,nilnvoid/wagtail,iansprice/wagtail,Toshakins/wagtail,inonit/wagtail,kurtrwall/wagtail,inonit/wagtail,jnns/wagtail,mikedingjan/wagtail,wagtail/wagtail,zerolab/wagtail,kurtw/wagtail,mikedingjan/wagtail,jnns/wagtail,torchbox/wagtail,thenewguy/wagtail,timorieber/wagtail,mixxorz/wagtail,chrxr/wagtail,FlipperPA/wagtail,gasman/wagtail,jnns/wagtail,mikedingjan/wagtail,JoshBarr/wagtail,nimasmi/wagtail,torchbox/wagtail,thenewguy/wagtail