Remove alias: picture -> photo_(object)

BUR #4075 has been approved by @evazion.

remove alias picture -> photo_(object)
remove alias pictures -> photo_(object)

Picture is a very ambiguous tag that could equally refer to photo (medium), photo (object), or painting (object).

EDIT: The bulk update request #4075 (forum #176732) has been approved by @evazion.

The bulk update request #4075 (forum #176732) has been approved by @evazion.