[analyzer] [NFC] Remove unused Extensive diagnostic setting,

Rename AlternateExtensive to Extensive.
In 2013, five years ago, we have switched to AlternateExtensive
diagnostics by default, and Extensive was available under unused,
undocumented flag.
This change remove the flag, renames the Alternate
diagnostic to Extensive (as it's no longer Alternate), and ports the
test.

Differential Revision: https://reviews.llvm.org/D47670

llvm-svn: 334524

clang/include/clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h

@@ -114,7 +114,16 @@ class PathDiagnosticConsumer {
 
   void HandlePathDiagnostic(std::unique_ptr<PathDiagnostic> D);
 
-  enum PathGenerationScheme { None, Minimal, Extensive, AlternateExtensive };
+  enum PathGenerationScheme {
+    /// Only runs visitors, no output generated.
+    None,
+
+    /// Used for HTML and text output.
+    Minimal,
+
+    /// Used for plist output, used for "arrows" generation.
+    Extensive,
+  };
 
   virtual PathGenerationScheme getGenerationScheme() const { return Minimal; }
   virtual bool supportsLogicalOpControlFlow() const { return false; }