fix: hide experimental settings for doc and folder icons (#15021)

should fix #13955
The emoji doc and folder icons have been officially released with v0.25
but the experimental settings were still available with no effect if
switched.

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## Summary by CodeRabbit

* **Chores**
* Feature flags for emoji folder and document icons are no longer
user-configurable.

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packages/frontend/core/src/modules/feature-flag/constant.ts

@@ -107,7 +107,7 @@ export const AFFINE_FLAGS = {
     feedbackType: 'discord',
     feedbackLink:
       'https://discord.com/channels/959027316334407691/1280014319865696351/1280014319865696351',
-    configurable: true,
+    configurable: false,
     defaultState: true,
   },
   enable_emoji_doc_icon: {
@@ -119,7 +119,7 @@ export const AFFINE_FLAGS = {
     feedbackType: 'discord',
     feedbackLink:
       'https://discord.com/channels/959027316334407691/1280014319865696351',
-    configurable: true,
+    configurable: false,
     defaultState: true,
   },
   enable_editor_settings: {