Log Message:
vym: Fix portability of man page installation.

This package actually honours PKGMANDIR and uses CMAKE_INSTALL_MANDIR
in the upstream code, but this was negated in several SUBSTs that
were inserted into the package Makefile, resulting in installation
failing on anything where PKGMANDIR isn't "man" (most things other
than NetBSD use "share/man").

Remove the SUBSTs and fix installation in another way.

See the pkgsrc guide for information on how MANCOMPRESSED can
handle .gz man pages automatically.