Remove Target/User validation from Block::appliesToUsertalk()

Remove Target/User validation from Block::appliesToUsertalk()

This fixes a regression in I0e131696419211319082cb454f4f05297e55d22e where
an IP block that also blocks logged in users from editing, throws an exception.

The target/user validation in Block::appliesToUsertalk() does not work well
when an IP block prevents logged in users from editing. This case throws a
validation error, when in reality it should make a judgement.

This change means that the method will now trust whatever is passed into it as
the current user's talk page.

Bug: T211578
Change-Id: I3bb27cf7bec8421d31aa4de28a0e658365bb5bf2