layers: Remove unneeded layer_common.h

The header only had one include in it.
diff --git a/layers/device_limits.h b/layers/device_limits.h
index 6f11c23..8575b90 100644
--- a/layers/device_limits.h
+++ b/layers/device_limits.h
@@ -23,7 +23,7 @@
  */
 #include "vk_layer.h"
 #include <vector>
-#include "layer_common.h"
+#include "vk_debug_report_lunarg.h"
 
 using namespace std;