Delete superfluous call feature settings code.

+ Remove superfluous voicemail provider null checks. Voicemail
provider always exists in the preferences which are added and is
never removed, so these null checks are unnecessary.

+ Remove unused class variables and functions.

Bug: 17019623
Change-Id: I5f9175ccb24f54e2e748938652f12b09bffa8fcc
1 file changed