[1.8.x] Removed query.alias_diff()
[1.8.x] Removed query.alias_diff()

This function is unused since 6fe2b001dba45134d7c10729c57959995e241a88

Backport of f79ce63fdb6788c8b4857fece6c86de57fc129ee from master

pquentin/django,h4r5h1t/django-hauthy,pquentin/django,h4r5h1t/django-hauthy,pquentin/django,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy