Remove unnecessary WRITE_SMS permission - framework

Currently only one app can write to the SMS provider and it has to
be set as the default SMS app by the user in the UI. The default
SMS app is set by enabling the write SMS app op for it and keeping
this op off for other SMS apps. Hence, this permission does not
guard anything and can be taken out. The API change is fine as if
an app refers to the permission in the manifest as string it will
be ignored and if it was referred in Java the value is statically
compiled in the source.

Change-Id: I1128c3b034e6c7dda4baa051500ac1ef46a53575