fdo#43637 Two commands with the same name "Backspace"

One of them emulates the "Backspace" and the other one "Shift+Backspace", so I renamed it accordingly

Change-Id: I8a2a9f2b5b7212d4ea385c3b5f2e47ac014accc3
Reviewed-on: https://gerrit.libreoffice.org/6887Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

officecfg/registry/data/org/openoffice/Office/UI/WriterCommands.xcu

@@ -1576,7 +1576,7 @@
       </node>
       <node oor:name=".uno:ShiftBackspace" oor:op="replace">
         <prop oor:name="Label" oor:type="xs:string">
-          <value xml:lang="en-US">Backspace</value>
+          <value xml:lang="en-US">Shift+Backspace</value>
         </prop>
       </node>
       <node oor:name=".uno:SelectWord" oor:op="replace">