[CodeCompletion] Remove unused forward declaration and fix up an out-of-date comment (NFC)

Author: Nathan Hawes

lib/IDE/CodeCompletion.cpp

@@ -1531,7 +1531,6 @@ void CodeCompletionContext::sortCompletionResults(
 }
 
 namespace {
-class CompletionLookup;
 
 class CodeCompletionCallbacksImpl : public CodeCompletionCallbacks {
   CodeCompletionContext &CompletionContext;

lib/Sema/TypeCheckCodeCompletion.cpp

@@ -739,9 +739,8 @@ bool TypeChecker::typeCheckForCodeCompletion(
   ContextFinder contextAnalyzer(expr);
   expr->walk(contextAnalyzer);
 
-  // If there was no completion expr (e.g. if the code completion location is
-  // within an ErrorExpr without an valid subexpr due to parser error recovery)
-  // bail.
+  // If there was no completion expr (e.g. if the code completion location was
+  // among tokens that were skipped over during parser error recovery) bail.
   if (!contextAnalyzer.hasCompletionExpr())
     return false;