Remove redundant casts. NFC

So I wrote a clang-tidy check to lint out redundant `isa`, `cast`, and
`dyn_cast`s for fun. This is a portion of what it found for clang; I
plan to do similar cleanups in LLVM and other subprojects when I find
time.

Because of the volume of changes, I explicitly avoided making any change
that wasn't highly local and obviously correct to me (e.g. we still have
a number of foo(cast<Bar>(baz)) that I didn't touch, since overloading
is a thing and the cast<Bar> did actually change the type -- just up the
class hierarchy).

I also tried to leave the types we were cast<>ing to somewhere nearby,
in cases where it wasn't locally obvious what we were dealing with
before.

llvm-svn: 326416
diff --git a/clang/lib/AST/TemplateBase.cpp b/clang/lib/AST/TemplateBase.cpp
index e81c11a..7ed6bf1 100644
--- a/clang/lib/AST/TemplateBase.cpp
+++ b/clang/lib/AST/TemplateBase.cpp
@@ -406,7 +406,7 @@
   }
     
   case Declaration: {
-    NamedDecl *ND = cast<NamedDecl>(getAsDecl());
+    NamedDecl *ND = getAsDecl();
     Out << '&';
     if (ND->getDeclName()) {
       // FIXME: distinguish between pointer and reference args?