Sync status bar signal cluster code with AOSP.

As AOSP now supports MSIM, there's no point in carrying a MSIM specific
code variant around, as doing so carries a large maintenance burden.
Consequently, our signal cluster code lagged significantly behind AOSP
and carried large chunks of unused legacy code.

Change-Id: Ibda6308e80c670d4dffcef21260cb7b84413e36c