[AST] Remove hasSyntaxRoot

Use `shouldBuildSyntaxTree` instead.

Author: hamishknight

include/swift/AST/SourceFile.h

@@ -582,7 +582,6 @@ class SourceFile final : public FileUnit {
   bool hasDelayedBodyParsing() const;
 
   syntax::SourceFileSyntax getSyntaxRoot() const;
-  bool hasSyntaxRoot() const;
 
   OpaqueTypeDecl *lookupOpaqueResultType(StringRef MangledName) override;
 

lib/AST/Module.cpp

@@ -1088,12 +1088,8 @@ void SourceFile::getInterfaceHash(llvm::SmallString<32> &str) const {
   llvm::MD5::stringifyResult(result, str);
 }
 
-bool SourceFile::hasSyntaxRoot() const {
-  return ParsingOpts.contains(ParsingFlags::BuildSyntaxTree);
-}
-
 syntax::SourceFileSyntax SourceFile::getSyntaxRoot() const {
-  assert(hasSyntaxRoot() && "has no syntax root");
+  assert(shouldBuildSyntaxTree() && "Syntax tree disabled");
   auto &eval = getASTContext().evaluator;
   auto *mutableThis = const_cast<SourceFile *>(this);
   return *evaluateOrDefault(eval, ParseSourceFileRequest{mutableThis}, {})