Revert "travis: Choose schema based on USE_OLD_SCHEMA file" (#1193)

This reverts commit a866c43.

Observe that there are no more USE_OLD_SCHEMA files in this repository.
This indicates that henceforth all canonical-data.json files should use
the schema proposed in
#996 and
defined in #1074.

.travis.yml

@@ -6,44 +6,4 @@ cache: yarn
 
 script:
   - bin/check_required_files_present
-  - |
-    invalid_old=""
-    invalid_new=""
-    forgotten=""
-
-    for json in exercises/*/canonical-data.json; do
-      dir=$(dirname $json)
-      ex=$(basename $dir)
-
-      if [ -f "$dir/USE_OLD_SCHEMA" ]; then
-        if ! ajv -s old-schema.json -d $json; then
-          invalid_old="$invalid_old $ex"
-        fi
-        # If we have converted to new,
-        # make sure we don't forget to remove USE_OLD_SCHEMA file!
-        if ajv -s canonical-schema.json -d $json 2>/dev/null; then
-          forgotten="$forgotten $ex"
-        fi
-      else
-        if ! ajv -s canonical-schema.json -d $json; then
-          invalid_new="$invalid_new $ex"
-        fi
-      fi
-    done
-
-    stat=0
-
-    if [ -n "$invalid_old" ]; then
-      echo "Exercises using old schema, but invalid: $invalid_old"
-      stat=1
-    fi
-    if [ -n "$invalid_new" ]; then
-      echo "Exercises using new schema, but invalid: $invalid_new"
-      stat=1
-    fi
-    if [ -n "$forgotten" ]; then
-      echo "Exercises using new schema, but forgot to remove USE_OLD_SCHEMA file: $forgotten"
-      stat=1
-    fi
-
-    exit $stat
+  - yarn test