graphics/timg: update to 1.6.0
Changelog: https://github.com/hzeller/timg/releases/tag/v1.6.0
Added WITH_POPPLER and WITH_RSVG to CMAKE_OFF.
Added pkgconfig to USES.
Pet portclippy.
Approved by: diizzy (mentor)
Differential Revision: https://reviews.freebsd.org/D43898