refactor(@angular-devkit/schematics): remove deprecated FileSystemHost

BREAKING CHANGE
Deprecated `FileSystemHost` has been removed. Use `Host` directly instead.

Note: this change only effects direct `@angular-devkit/schematics` users and not the application developers.

Author: alan-agius4

etc/api/angular_devkit/schematics/tools/index.d.ts

@@ -74,10 +74,6 @@ export declare abstract class FileSystemEngineHostBase implements FileSystemEngi
     transformOptions<OptionT extends object, ResultT extends object>(schematic: FileSystemSchematicDesc, options: OptionT, context?: FileSystemSchematicContext): Observable<ResultT>;
 }
 
-export declare class FileSystemHost extends virtualFs.ScopedHost<{}> {
-    constructor(dir: string);
-}
-
 export declare type FileSystemSchematic = Schematic<FileSystemCollectionDescription, FileSystemSchematicDescription>;
 
 export declare type FileSystemSchematicContext = TypedSchematicContext<FileSystemCollectionDescription, FileSystemSchematicDescription>;

packages/angular_devkit/schematics/tools/file-system-host.ts

@@ -8,7 +8,6 @@
 export * from './description';
 export * from './export-ref';
 export * from './file-system-engine-host-base';
-export * from './file-system-host';
 
 export * from './workflow/node-workflow';