poppler: let's disable Qt5 too

Change-Id: I8571aa0ccc9f691d7fd9290a647117161755d3a7
(cherry picked from commit aaf717a8fad0b097b84cbd803acea1330bd925a5)
Reviewed-on: https://gerrit.libreoffice.org/13485
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>