De-ASTContext-ify DeclContext.

Remove ASTContext parameter from DeclContext's methods. This change cascaded down to other Decl's methods and changes to call sites started "escalating".
Timings using pre-tokenized "cocoa.h" showed only a ~1% increase in time run between and after this commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74506 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/DeclXML.cpp b/lib/Frontend/DeclXML.cpp
index dcc9cea..68f931f 100644
--- a/lib/Frontend/DeclXML.cpp
+++ b/lib/Frontend/DeclXML.cpp
@@ -34,8 +34,8 @@
 
   void addSubNodes(RecordDecl* RD)
   {
-    for (RecordDecl::field_iterator i = RD->field_begin(*Doc.Ctx), e = RD->field_end(*Doc.Ctx); i != e; ++i)
-    {
+    for (RecordDecl::field_iterator i = RD->field_begin(),
+                                    e = RD->field_end(); i != e; ++i) {
       Visit(*i);
       Doc.toParent();
     }
@@ -43,8 +43,8 @@
 
   void addSubNodes(EnumDecl* ED)
   {
-    for (EnumDecl::enumerator_iterator i = ED->enumerator_begin(*Doc.Ctx), e = ED->enumerator_end(*Doc.Ctx); i != e; ++i)
-    {
+    for (EnumDecl::enumerator_iterator i = ED->enumerator_begin(),
+                                       e = ED->enumerator_end(); i != e; ++i) {
       Visit(*i);
       Doc.toParent();
     }