graphics/zathura-pdf-mupdf: update to 0.4.2

The project moved to github but can use official tarballs so set
MASTER_SITES variable and remove USE_GITLAB.

Changelog:

• fix zathura crashing when :info is run on a non-PDF document
• fix initialization if link target

PR: 279411
Approved by: bofh (implicit), diizzy (implicit)