Remove CBasicBridging and CASTBridging

Merge with BasicBridging and ASTBridging
respectively. The changes here should be pretty
uncontroversial, I tried to keep it to just moving
code about.

include/module.modulemap

@@ -4,20 +4,12 @@ module BasicBridging {
   export *
 }
 
-module CBasicBridging {
-  header "swift/Basic/CBasicBridging.h"
-}
-
 module ASTBridging {
   header "swift/AST/ASTBridging.h"
   requires cplusplus
   export *
 }
 
-module CASTBridging {
-  header "swift/AST/CASTBridging.h"
-}
-
 module SILBridging {
   header "swift/SIL/SILBridging.h"
   requires cplusplus