replace boost::bimap in sdext pdfimport

replace boost::bimap in sdext pdfimport

the error message with boost 1.69 and gcc 10 is so ungodly its easier to throw
bimap out and use something simpler

Change-Id: Ie324a0b81931bbd427483878a87beeca455ada18
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/87683
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Gbp-Pq: Name gcc10-replace-boost::bimap-in-sdext.diff