Fix MediaDescriptor.idl for TemplateRegionName

Clearly Cut & Paste slipped into this file.

Please review the correct content for TemplateRegionName

Change-Id: Ic3c896f13c204f28a231e442d3dd68a4b33373f1
Reviewed-on: https://gerrit.libreoffice.org/11282
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>