docs(cheatsheet): complete the copy edit (#11215)

…and general cleanup of the cheatsheet.

modules/@angular/docs/cheatsheet/forms.md

@@ -4,10 +4,9 @@ Forms
 @description
 {@target ts}`import { FormsModule } from '@angular/forms';`{@endtarget}
 {@target js}Available using the `ng.forms.FormsModule` module{@endtarget}
-{@target dart}Available using `platform_directives` in pubspec{@endtarget}
 
 @cheatsheetItem
 syntax:
 `<input [(ngModel)]="userName">`|`[(ngModel)]`
 description:
-Provides two-way data-binding, parsing and validation for form controls.
+Provides two-way data-binding, parsing, and validation for form controls.