Revert "libgui: Make bq_gl_fence_cleanup a bugfix flag"

This reverts commit 95c4948.

Reason for revert: Turns out you can't do this >:(

Change-Id: Ib267951ab8956f834a4a2c8bc0a45f134531f5c1

Author: Jim Shargo

libs/gui/libgui_flags.aconfig

@@ -138,7 +138,4 @@ flag {
   description: "Remove BufferQueueProducer::dequeue's wait on this fence (or the fence entirely) to prevent deadlocks"
   bug: "339705065"
   is_fixed_read_only: true
-  metadata {
-    purpose: PURPOSE_BUGFIX
-  }
 } # bq_gl_fence_cleanup