[analyzer] ConditionBRVisitor: Remove GDM checking

Summary: Removed the `GDM` checking what could prevent reports made by this visitor. Now we rely on constraint changes instead.

Reviewers: NoQ, george.karpenkov

Reviewed By: NoQ

Subscribers: jdoerfert, gerazo, xazax.hun, baloghadamsoftware, szepet, a.sidorin, mikhail.ramalho, Szelethus, donat.nagy, dkrupp

Tags: #clang

Differential Revision: https://reviews.llvm.org/D54811

llvm-svn: 356318