docs: Backup requestRestore() doesn't kill app during restore.

Doc-only change to note that requestRestore() doesn't behave as expected
and kill the app as part of the restore operation.
Fixed formatting of first paragraph running into deprecation notice.
Also removed dupe versioning info from deprecation notice--see staged version.
Staged at:
  http://go/dac-stage/reference/android/app/backup/BackupManager#requestrestore

Bug: 29255593
Test: make ds-docs and staged output. Visual inspection and manual link test.
Change-Id: I8baae2216f23bd63510f8b445fcdd8090354b0df