refactor(@ngtools/webpack): remove deprecated isSupported method

BREAKING CHANGE:
`isSupported` method has been removed from `AngularCompilerPlugin` as it has become redundant with peer dependencies.

Note: this change only effects direct `@ngtools/webpack` users and not the application developers.

packages/ngtools/webpack/src/angular_compiler_plugin.ts

@@ -24,7 +24,6 @@ import {
   Program,
   SOURCE,
   UNKNOWN_ERROR_CODE,
-  VERSION,
   createCompilerHost,
   createProgram,
   formatDiagnostics,
@@ -156,11 +155,6 @@ export class AngularCompilerPlugin {
     return tsProgram ? tsProgram.getTypeChecker() : null;
   }
 
-  /** @deprecated  From 8.0.2 */
-  static isSupported() {
-    return VERSION && parseInt(VERSION.major) >= 8;
-  }
-
   private _setupOptions(options: AngularCompilerPluginOptions) {
     time('AngularCompilerPlugin._setupOptions');
     this._logger = options.logger || createConsoleLogger();