BUG 2970 : Recovery fails with SchemaValidationException when removing modules

BUG 2970 : Recovery fails with SchemaValidationException when removing modules

My prior fixes for bug 2970 did not address the recovery problem when a module is
removed but it's data is still present in the persisted files. This patch attempts
to address that.

There seems to be no schema validation when you write a normalized node at / so
for when writing or merging at / the pruning is done first before attempting a
write on InMemoryDataTreeModification

Also removed all unneccessary code.

Change-Id: Id2793330441606c62dfd903cdd698c2f86b14c1b
Signed-off-by: Moiz Raja <moraja@cisco.com>