[libSyntax] Remove the C++ SyntaxClassifier

The recommended way forward is to use the SyntaxClassifier on the Swift
side.

By removing the C++ SyntaxClassifier, we can also eliminate the
-force-libsyntax-based-processing option that was used to bootstrap
incremental parsing and would generate the syntax map from a syntax
tree.

utils/gyb_sourcekit_support/UIDs.py

@@ -49,7 +49,6 @@ UID_KEYS = [
     KEY('SerializedSyntaxTree', 'key.serialized_syntax_tree'),
     KEY('SyntaxReuseRegions', 'key.syntaxreuseregions'),
     KEY('SourceText', 'key.sourcetext'),
-    KEY('ForceLibSyntaxBasedProcessing', 'key.forcelibsyntaxbasedprocessing'),
     KEY('EnableSyntaxReuseRegions', 'key.enablesyntaxreuseregions'),
     KEY('EnableSyntaxMap', 'key.enablesyntaxmap'),
     KEY('SyntaxTreeTransferMode', 'key.syntaxtreetransfermode'),