Base JWT service endpoint choice directly on the MatrixRTC mode

Since we removed the extra 'legacy' mode, meaning there's nothing simplified anymore by translating things over to a JWT service version.

(Also, simplify some things by making the mode static for the duration of a call.)

src/utils/observable.ts

@@ -227,38 +227,6 @@ export function filterBehavior<T, S extends T>(
     );
 }
 
-/**
- * Maps a changing input value to an item whose lifetime is tied to a certain
- * computed key. The item may capture some dynamic data from the input.
- */
-export function generateItem<
-  Input,
-  Keys extends [unknown, ...unknown[]],
-  Data,
-  Item,
->(
-  name: string,
-  generator: (input: Input) => { keys: readonly [...Keys]; data: Data },
-  factory: (
-    scope: ObservableScope,
-    data$: Behavior<Data>,
-    ...keys: Keys
-  ) => Item,
-): OperatorFunction<Input, Item> {
-  return (input$) =>
-    input$.pipe(
-      generateItemsInternal(
-        name,
-        function* (input) {
-          yield generator(input);
-        },
-        factory,
-        (items) => items,
-      ),
-      map(([item]) => item),
-    );
-}
-
 function generateItemsInternal<
   Input,
   Keys extends [unknown, ...unknown[]],

src/utils/test-viewmodel.ts

@@ -174,7 +174,7 @@ export function getBasicCallViewModelEnvironment(
           setE2EEEnabled: async () => Promise.resolve(),
         }),
       connectionState$: constant(ConnectionState.Connected),
-      matrixRTCMode$: constant(MatrixRTCMode.Compatibility),
+      matrixRTCMode: MatrixRTCMode.Compatibility,
       ...callViewModelOptions,
     },
     handRaisedSubject$,