Chore: Adapt #60, #64 in line with other breaking changes.

This commit undoes #64 (and bumps the library MSRV accordingly), and modifies #60 to match the new `Call` connection handling.

This was tested using `cargo make ready`, and rustc v1.49.0 on `examples/serenity/voice`.

Cargo.toml

@@ -85,11 +85,6 @@ version = "0.1"
 optional = true
 version = "1"
 
-# TEMPORARY: remove on next breaking.
-[dependencies.spinning_top]
-optional = true
-version = "=0.2.2"
-
 [dependencies.streamcatcher]
 optional = true
 version = "0.1"
@@ -153,7 +148,6 @@ gateway-core = [
     "flume",
     "parking_lot",
     "pin-project",
-    "spinning_top",
 ]
 driver = [
     "async-tungstenite",
@@ -177,7 +171,6 @@ driver-core = [
     "rand",
     "serenity-voice-model",
     "spin_sleep",
-    "spinning_top",
     "streamcatcher",
     "typemap_rev",
     "url",