partially revert ofz#11275 erase via position

partial revert of:
commit e8833d4d
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Mon Jan 21 09:33:04 2019 +0000

because of the concerns of https://gerrit.libreoffice.org/#/c/66665/ i.e.
"this looks like it reintroduces the bug fixed in
 471212d4"

but continue to erase the final entry by its known index, rather than force a
lookup of the index of the final entry

Change-Id: Ic14aa133779b5555e8856d6c8fefe4e9b854e2fa

sw/source/core/doc/docredln.cxx

@@ -623,11 +623,10 @@ void SwRedlineTable::Remove( size_type nP )
 
 void SwRedlineTable::DeleteAndDestroyAll()
 {
-    auto nCount = maVector.size();
-    while (nCount)
+    while (!maVector.empty())
     {
         auto const pRedline = maVector.back();
-        maVector.erase(--nCount);
+        maVector.erase(maVector.size() - 1);
         LOKRedlineNotification(RedlineNotification::Remove, pRedline);
         delete pRedline;
     }