refactor(@angular/cli): remove deprecated command aliases for extract-i18n.

BREAKING CHANGE:

Deprecated `ng x18n` and `ng i18n-extract` commands have been removed in favor of `ng extract-i18n`.

Author: alan-agius4

packages/angular/cli/commands/extract-i18n-impl.ts

@@ -24,14 +24,6 @@ export class ExtractI18nCommand extends ArchitectCommand<ExtractI18nCommandSchem
       return 1;
     }
 
-    const commandName = process.argv[2];
-    if (['xi18n', 'i18n-extract'].includes(commandName)) {
-      this.logger.warn(
-        `Warning: "ng ${commandName}" has been deprecated and will be removed in a future major version. ` +
-          'Please use "ng extract-i18n" instead.',
-      );
-    }
-
     return this.runArchitectTarget(options);
   }
 }

packages/angular/cli/commands/extract-i18n.json

@@ -3,8 +3,6 @@
   "$id": "ng-cli://commands/extract-i18n.json",
   "description": "Extracts i18n messages from source code.",
   "$longDescription": "",
-
-  "$aliases": ["i18n-extract", "xi18n"],
   "$scope": "in",
   "$type": "architect",
   "$impl": "./extract-i18n-impl#ExtractI18nCommand",