Update SwDoc::Paste from SwFEShell::Paste

SwDoc::Paste is already an minimal version of SwFEShell::Paste.

Update the code based on the changes made in
    commit 4580094d2d9d5b952c4526ee23204f75a5bb2f1b

Change-Id: I4d784f393952374e2a174510f9378b05cfdb78eb
Reviewed-on: https://gerrit.libreoffice.org/9861
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>