Layouts: Remove unused plugin.json

Change-Id: I5d1eb1c46617d15e22b6d542f14e1b2d8e213f5e
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>

src/layouts/layouts.pro

@@ -20,7 +20,4 @@ HEADERS += \
     qquicklayout_p.h \
     qquicklinearlayout_p.h
 
-OTHER_FILES += \
-    $$PWD/plugin.json
-
 load(qml_plugin)

src/layouts/plugin.json

-{}