Reset restricted count on merge.

This will prevent merged conference having participant with name as following:
1. Restrict and non-restriced
"<phone number or name>"
"Restricted 2"

2. Two restricted number
"Restricted 3"
"Restricted 4"

After the change it will become:
case 1:
"<phone number or name>"
"Restricted"

case 2:
"Restricted 1"
"Restricted 2"

Note: Unfortunately there isn't a way to relate the pre-merge restricted calls to the post-merge restricted calls. So "Restricted 2" is not necessary the one pre-merge. This also means reset is safe here for merge.
Bug: 63315372
Test: manual
PiperOrigin-RevId: 161267675
Change-Id: I2df16b6f9802932c06f0bdd62618c49f4e6e87a8