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

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -135,52 +135,11 @@ externalData(
     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.