rename legacy_icu tokenizer to icu tokenizer

The new icu tokenizer is now no longer compatible with the old
legacy tokenizer in terms of data structures. Therefore there
is also no longer a need to refer to the legacy tokenizer in the
name.

test/bdd/steps/steps_db_ops.py

@@ -280,7 +280,7 @@ def check_word_table_for_postcodes(context, exclude, postcodes):
     plist.sort()
 
     with context.db.cursor(cursor_factory=psycopg2.extras.DictCursor) as cur:
-        if nctx.tokenizer == 'legacy_icu':
+        if nctx.tokenizer == 'icu':
             cur.execute("SELECT word FROM word WHERE type = 'P' and word = any(%s)",
                         (plist,))
         else: