Contacts : Remove silent option from ringtone

Silent is fundamentally broken across the platform, its currently
the same as default anyway. A lot of assumptions are based on this
"bug" such as default multi-sim ringtones...etc

Remove the option for now as it doesn't work anyway.

Issue-id: FEIJ-939
Change-Id: I3ce669c8c5f078349054faa0eb29486a3755ce43