[Swift] Remove unused include (#1962)

apple-llvm-split-commit: a6d1da3006eacf23a802b79f12d8b4de33074a11
apple-llvm-split-dir: lldb/

Author: jrose-apple

lldb/source/Symbol/SwiftASTContext.cpp

@@ -49,7 +49,6 @@
 #include "swift/Frontend/PrintingDiagnosticConsumer.h"
 #include "swift/IRGen/Linking.h"
 #include "swift/SIL/SILModule.h"
-#include "swift/Serialization/ModuleFile.h"
 #include "swift/Serialization/Validation.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclObjC.h"