Simplify Weak Lever

Simplify Weak Lever

This is a simplification that integrated WeakLever into doubled pawns.
Since we already check for !support for Doubled pawns, it is trivial
to check for weak lever by just checking more_than_one(lever).

We also introduce the Score * bool operation overload to remove some
casts in the code.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 26757 W: 5842 L: 5731 D: 15184
http://tests.stockfishchess.org/tests/view/5d77ee220ebc5902d384e5a4

Closes https://github.com/official-stockfish/Stockfish/pull/2295

No functional change