Remove unused parameter from CXXRecordDecl::forallBases [NFC]

Summary:
Apparently all users of the function were fine with short-circuiting
and none cared to override the default argument.

Reviewers: aaron.ballman, rsmith

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75319