Restructure virt-backup-restore-snapshots.adoc to remove text from between include statements.

Line 1: Assign [role="_abstract"] to a paragraph to use it as  <shortdesc> in DITA. 

Line 36: Content other than additional resources cannot follow include directives.  
Lines 109, 145: Remove callouts

See https://docs.google.com/spreadsheets/d/1vLrFYdKphcFLoWNEH3E4oCJ2HsOUDLQ72yFnfiYNnXU/edit?gid=503904153#gid=503904153