www/bluefish: Do not bundle MIME database files

Instead, the MIME database files will be created as a post-install
step thanks to USES=desktop-file-utils and USES=shared-mime-info.

This prevents the bluefish package (and other packages) from clobbering
the local MIME database, causing package conflicts and checksum
mismatches.
https://lists.freebsd.org/pipermail/freebsd-ports/2017-March/107752.html

Reported by: Werner Lehmann <lehmannwer@gmail.com>
Reported by: tech-lists@zyxst.net
Submitted by: tijl
MFH: 2019Q2