[analyzer] ConditionBRVisitor: Remove duplicated code

Summary: -

Reviewers: NoQ, george.karpenkov

Reviewed By: NoQ

Subscribers: cfe-commits, xazax.hun, baloghadamsoftware, szepet, a.sidorin,
             mikhail.ramalho, Szelethus, donat.nagy, dkrupp

Tags: #clang

Differential Revision: https://reviews.llvm.org/D58199

llvm-svn: 362025