Remove one of SanitizerBlacklist::isIn() overloads. NFC.

The final goal is to get rid of all the rest overloads that
accept LLVM objects (llvm::Function and llvm::GlobalVariable),
and pass in source-level entities instead.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219937 91177308-0d34-0410-b5e6-96231b3b80d8