[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/UndefResultChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
index 47faf69..f30f32e 100644
--- a/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
@@ -174,10 +174,10 @@
     auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N);
     if (Ex) {
       report->addRange(Ex->getSourceRange());
-      bugreporter::trackNullOrUndefValue(N, Ex, *report);
+      bugreporter::trackExpressionValue(N, Ex, *report);
     }
     else
-      bugreporter::trackNullOrUndefValue(N, B, *report);
+      bugreporter::trackExpressionValue(N, B, *report);
 
     C.emitReport(std::move(report));
   }