[Form] Removed the "disabled" attribute from the placeholder option in select fields due to problems with the BlackBerry 10 browser

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7678 #8478 #8526
| License       | MIT
| Doc PR        | -