mesh: Fix LPN subsciption groups update on VA deletion
mesh: Fix LPN subsciption groups update on VA deletion

This fixes missing bt_mesh_lpn_group_del call in mod_sub_va_del.
If Config Model Subscription Virtual Address Delete was received
and successfully proceeded, subscription address shall be also
deleted from LPN Subscribe Groups.

mlaz/mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/incubator-mynewt-core,andrzej-kaczmarek/apache-mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,andrzej-kaczmarek/apache-mynewt-core