[CodeCompletion] Support a narrow case for producing trailing closures directly

This adds a narrow special case in code-completion for control-flow-like
methods such as DispatchQueue().sync that are () -> (), to add a new
completion where the trailing closure is immediately expanded rather
than having to invoke placeholder expansion as a second step.

rdar://problem/26628804

lib/Sema/ConstraintSystem.h

@@ -2131,43 +2131,6 @@ static inline bool computeTupleShuffle(TupleType *fromTuple,
 /// trailing closure.
 bool hasTrailingClosure(const ConstraintLocatorBuilder &locator);
 
-/// A call argument or parameter.
-struct LLVM_LIBRARY_VISIBILITY CallArgParam {
-  /// The type of the argument or parameter. For a variadic parameter,
-  /// this is the element type.
-  Type Ty;
-
-  // The label associated with the argument or parameter, if any.
-  Identifier Label;
-
-  /// Whether the parameter has a default argument.  Not valid for arguments.
-  bool HasDefaultArgument = false;
-
-  /// Whether the parameter is variadic. Not valid for arguments.
-  bool Variadic = false;
-
-  /// Whether the argument or parameter has a label.
-  bool hasLabel() const { return !Label.empty(); }
-};
-
-/// Break an argument type into an array of \c CallArgParams.
-///
-/// \param type The type to decompose.
-SmallVector<CallArgParam, 4> decomposeArgType(Type type);
-
-/// Break a parameter type into an array of \c CallArgParams.
-///
-/// \param paramOwner The declaration that owns this parameter.
-/// \param level The level of parameters that are being decomposed.
-SmallVector<CallArgParam, 4> decomposeParamType(
-                               Type type,
-                               ValueDecl *paramOwner,
-                               unsigned level);
-
-/// Turn a param list into a symbolic and printable representation that does not
-/// include the types, something like (: , b:, c:)
-std::string getParamListAsString(ArrayRef<CallArgParam> parameters);
-
 /// Describes the arguments to which a parameter binds.
 /// FIXME: This is an awful data structure. We want the equivalent of a
 /// TinyPtrVector for unsigned values.