sysutils/vimpager: Fix build when DOCS option turned off

Download generated man pages from master site and add DIST_SUBDIR
variable.
Remove TEST option (it was a misunderstood).
Add conditionally patch which remove generation of documentation and the warning
message about missing pandoc.

PR: 287571
Reported by: Anton Saietskii <vsasjason@gmail.com>
Approved by: Yusuf Yaman <nxjoseph@protonmail.com> (maintainer)