C++: Remove some unused legacy relations from the DB scheme

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -122,65 +122,11 @@ compilation_finished(
     float elapsed_seconds : float ref
 );
 
-
-/**
- * External data, loaded from CSV files during snapshot creation. See
- * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
- * for more information.
- */
-externalData(
-    int id : @externalDataElement,
-    string path : string ref,
-    int column: int ref,
-    string value : string ref
-);
-
-/**
- * The date of the snapshot.
- */
-snapshotDate(unique date snapshotDate : date ref);
-
 /**
  * The source location of the snapshot.
  */
 sourceLocationPrefix(string prefix : string ref);
 
-/**
- * Data used by the 'duplicate code' detection.
- */
-duplicateCode(
-    unique int id : @duplication,
-    string relativePath : string ref,
-    int equivClass : int ref
-);
-
-/**
- * Data used by the 'similar code' detection.
- */
-similarCode(
-    unique int id : @similarity,
-    string relativePath : string ref,
-    int equivClass : int ref
-);
-
-/**
- * Data used by the 'duplicate code' and 'similar code' detection.
- */
-@duplication_or_similarity = @duplication | @similarity
-
-/**
- * Data used by the 'duplicate code' and 'similar code' detection.
- */
-#keyset[id, offset]
-tokens(
-    int id : @duplication_or_similarity ref,
-    int offset : int ref,
-    int beginLine : int ref,
-    int beginColumn : int ref,
-    int endLine : int ref,
-    int endColumn : int ref
-);
-
 /**
  * Information about packages that provide code used during compilation.
  * The `id` is just a unique identifier.