No longer display the number of rows shown on Special:Watchlist

My rationale for doing this is that passing this several functions
down is awkward and arguably bad design.

It's still a better rationale than the one used to add this in 2004,
which was replacing another value to fix HTML injection bug (r4728).

Change-Id: Iada3a93762dd25fdaf35fb707304abc40bd4a5b1