Bug 1894239: Enable MOZ_SELECTABLE_PROFILES by default. r=jhirsch,omc-reviewers,niklas,emcminn,mconley

This also removes some tests of `MOZ_SELECTABLE_PROFILES` from `browser/components/profiles` files
where the test is pointless because that test is excluded from the build if `MOZ_SELECTABLE_PROFILES`
is unset.

Differential Revision: https://phabricator.services.mozilla.com/D227372

browser/components/profiles/SelectableProfileService.sys.mjs

@@ -118,6 +118,13 @@ class SelectableProfileServiceClass {
     this.#asyncShutdownBlocker = () => this.uninit();
   }
 
+  get isEnabled() {
+    return (
+      Services.prefs.getBoolPref("browser.profiles.enabled", false) &&
+      !!(this.#storeID || this.#groupToolkitProfile)
+    );
+  }
+
   /**
    * For use in testing only, override the profile service with a mock version
    * and reset state accordingly.
@@ -258,6 +265,10 @@ class SelectableProfileServiceClass {
       );
     }
 
+    if (!this.isEnabled) {
+      return;
+    }
+
     // If the storeID doesn't exist, we don't want to create the db until we
     // need to so we early return.
     if (!this.storeID) {