Remove unreachable that was reached in modernize-use-nullptr.

Summary: When traversing the parent map, the check assumed that all the nodes would be either Stmt or Decl. After r251101, this is no longer true: there can be TypeLoc and NestedNameSpecifierLoc nodes.

Reviewers: alexfh

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D14229

llvm-svn: 251803