[Thread] remove thread_user_restriction_enabled

this flag is moved to frmeworks/base.

Bug: 319044650
Bug: 321624552
Change-Id: Ic068eb5e3cd2a7b4898a4f9a33b24ed8eed661f3
diff --git a/thread/flags/thread_base.aconfig b/thread/flags/thread_base.aconfig
index f73ea6b..bf1f288 100644
--- a/thread/flags/thread_base.aconfig
+++ b/thread/flags/thread_base.aconfig
@@ -6,10 +6,3 @@
     description: "Controls whether the Android Thread feature is enabled"
     bug: "301473012"
 }
-
-flag {
-    name: "thread_user_restriction_enabled"
-    namespace: "thread_network"
-    description: "Controls whether user restriction on thread networks is enabled"
-    bug: "307679182"
-}