Removed HOTPLUG=1 from the monitor hotplug rules.

Since udev didn't understand this key, it wasn't using it anyway.
This gets rid of the confusing error message in /var/log/messages.

TEST=Plugged/unplugged a VGA monitor and made sure modes still switched.

...also, built with FEATURES=keepwork and checked this file:

...validated that the unknown key was actually being ignored by udev, so this doesn't change behavior (other than getting rid of the error message).

Review URL:

Change-Id: I20fa098407299b0f0ff5cf06e95089fa0c8a7f5a
diff --git a/99-monitor-hotplug.rules b/99-monitor-hotplug.rules
index 77cefa7..37d6983 100644
--- a/99-monitor-hotplug.rules
+++ b/99-monitor-hotplug.rules
@@ -1,2 +1,2 @@
 # Reconfigure display output when the external monitor is [un]plugged.
-ACTION=="change", SUBSYSTEM=="drm", HOTPLUG=="1", RUN+=""
+ACTION=="change", SUBSYSTEM=="drm", RUN+=""