Bug 1899299 [Linux] Remove mRetryPointerGrab as it's unused r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D216911

widget/gtk/nsWindow.cpp

@@ -405,7 +405,6 @@ nsWindow::nsWindow()
       mIsAlert(false),
       mWindowShouldStartDragging(false),
       mHasMappedToplevel(false),
-      mRetryPointerGrab(false),
       mPanInProgress(false),
       mTitlebarBackdropState(false),
       mIsChildWindow(false),

widget/gtk/nsWindow.h

@@ -674,7 +674,6 @@ class nsWindow final : public nsBaseWidget {
   bool mIsAlert : 1;
   bool mWindowShouldStartDragging : 1;
   bool mHasMappedToplevel : 1;
-  bool mRetryPointerGrab : 1;
   bool mPanInProgress : 1;
   // Draw titlebar with :backdrop css state (inactive/unfocused).
   bool mTitlebarBackdropState : 1;