[analyzer] Rename trackNullOrUndefValue to trackExpressionValue

trackNullOrUndefValue is a long and confusing name,
and it does not actually reflect what the function is doing.
Give a function a new name, with a relatively clear semantics.

Also remove some dead code.

Differential Revision: https://reviews.llvm.org/D52758

llvm-svn: 345064
diff --git a/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
index a6b50dc..baf9aa0 100644
--- a/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/UnixAPIChecker.cpp
@@ -314,7 +314,7 @@
   auto report = llvm::make_unique<BugReport>(*BT_mallocZero, os.str(), N);
 
   report->addRange(arg->getSourceRange());
-  bugreporter::trackNullOrUndefValue(N, arg, *report);
+  bugreporter::trackExpressionValue(N, arg, *report);
   C.emitReport(std::move(report));
 
   return true;