Remove greyshade submodule entry

The theme has been replaced by cleanpress.

Change-Id: Ia5636f65a4682c4adc8584c94999ab6cafe5e540
Reviewed-on: https://gerrit.causes.com/23036
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>