Bug 1633855 - Clean up some old getSupportedFeatures actor compatibility; r=julienw

This is a drive-by clean-up, as I was touching this code.

Differential Revision: https://phabricator.services.mozilla.com/D76510

devtools/client/performance-new/@types/perf.d.ts

@@ -60,9 +60,6 @@ export interface PerfFront {
   on: (type: string, listener: () => void) => void;
   off: (type: string, listener: () => void) => void;
   destroy: () => void,
-  /**
-   * This method was was added in Firefox 72.
-   */
   getSupportedFeatures: () => MaybePromise<string[]>
 }
 
@@ -227,11 +224,8 @@ export interface InitializedValues {
   pageContext: PageContext;
   // The popup and devtools panel use different codepaths for getting symbol tables.
   getSymbolTableGetter: (profile: MinimallyTypedGeckoProfile) => GetSymbolTableCallback;
-  // The list of profiler features that the current target supports. Note that
-  // this value is only null to support older Firefox browsers that are targeted
-  // by the actor system. This compatibility can be required when the ESR version
-  // is running at least Firefox 72.
-  supportedFeatures: string[] | null
+  // The list of profiler features that the current target supports.
+  supportedFeatures: string[]
   // Allow different devtools contexts to open about:profiling with different methods.
   // e.g. via a new tab, or page navigation.
   openAboutProfiling?: () => void,
@@ -288,7 +282,7 @@ export type Action =
       openRemoteDevTools?: () => void,
       recordingSettingsFromPreferences: RecordingStateFromPreferences;
       getSymbolTableGetter: (profile: MinimallyTypedGeckoProfile) => GetSymbolTableCallback;
-      supportedFeatures: string[] | null;
+      supportedFeatures: string[];
     }
   | {
       type: "CHANGE_PRESET";
@@ -303,7 +297,7 @@ export interface InitializeStoreValues {
   presets: Presets;
   pageContext: PageContext;
   recordingPreferences: RecordingStateFromPreferences;
-  supportedFeatures: string[] | null;
+  supportedFeatures: string[];
   getSymbolTableGetter: (profile: MinimallyTypedGeckoProfile) => GetSymbolTableCallback;
   openAboutProfiling?: () => void;
   openRemoteDevTools?: () => void;

devtools/client/performance-new/components/Settings.js

@@ -11,7 +11,7 @@
  * @property {string[]} threads
  * @property {string} threadsString
  * @property {string[]} objdirs
- * @property {string[] | null} supportedFeatures
+ * @property {string[]} supportedFeatures
  */
 
 /**

devtools/client/performance-new/store/selectors.js

@@ -141,7 +141,7 @@ const getPageContext = state => getInitializedValues(state).pageContext;
 const getSymbolTableGetter = state =>
   getInitializedValues(state).getSymbolTableGetter;
 
-/** @type {Selector<string[] | null>} */
+/** @type {Selector<string[]>} */
 const getSupportedFeatures = state =>
   getInitializedValues(state).supportedFeatures;
 

devtools/shared/performance-new/gecko-profiler-interface.js

@@ -235,7 +235,6 @@ class ActorReadyGeckoProfilerInterface {
 
   /**
    * Lists the supported features of the profiler for the current browser.
-   * This method was added in Firefox 72.
    * @returns {string[]}
    */
   getSupportedFeatures() {