Mms: Do not show tips again when replace any attachment with Contact vCard

The method removeAttachment(false) will change the value of mMmsState,
so the toast will show again when the mMmsState change.

Remove the method removeAttachment() to make sure tips will not show
more than once when replace any attachment with Contact vCard in mms.

CRs-Fixed: 669194

Change-Id: Ib0f07a8c4501ee691c3d96b55b215f4d01d28593