[Sb refactor] Remove MobileConnectionModel

Rationale: MobileConnectionModel was loosely a representative data
object for the colletion of TelephonyCallbacks that we register on a
per-subscription basis. However, this data object only existed in the
boundary between MobileConnectionRepository -> MobileIconInteractor, and
was immediately unboxed into the relevant fields for use in business
logic. This meant that the entire object was being collected even if a
downstream client only relied on one field.

Ultimately, this leads to extra work being done, and extra logs being
written (e.g., DataActivity logs heppning even when the config to show
the activity was false).

The objective of this CL is _only_ to unbox the fields from
MobileConnectionModel, and to represent each field as a separate
property on the connection directly. The underlying implementation still
registers only a single callback with every listener, but the repository
breaks out every callback into its own flow immediately.

Test: test in com.android.systemui.statusbar.pipeline.mobile
Bug: 270300839
Change-Id: I8b62ae3367643143c6f36b689c65ab40e65c4510