Promote "history sharing on invite" out of developer options (#6647)

* Enable history sharing by default, unconditionally

* Remove feature-flag dep from history viz icons in room header

* Remove feature-flag dep from warning on inviting new people

* Remove feature-flag dep from warning on starting chat with new people

* Remove `enableKeyShareOnInvite` feature flag

* Update screenshots

* Remove redundant `FakeFeatureFlagService()` invocation, per review comment

---------

Co-authored-by: ElementBot <android@element.io>

libraries/featureflag/api/src/main/kotlin/io/element/android/libraries/featureflag/api/FeatureFlags.kt

@@ -52,17 +52,6 @@ enum class FeatureFlags(
         defaultValue = { false },
         isFinished = false,
     ),
-    EnableKeyShareOnInvite(
-        key = "feature.enableKeyShareOnInvite",
-        title = "Share encrypted history with new members",
-        description = "When inviting a user to an encrypted room that has history visibility set to \"shared\"," +
-            " share encrypted history with that user, and accept encrypted history when you are invited to such a room." +
-            "\nRequires an app restart to take effect." +
-            "\n\nWARNING: this feature is EXPERIMENTAL and not all security precautions are implemented." +
-            " Do not enable on production accounts.",
-        defaultValue = { false },
-        isFinished = false,
-    ),
     Knock(
         key = "feature.knock",
         title = "Ask to join",