Log Message:
pkgtools/pkglint4: remove some unreliable checks

The warnings about variable permissions were not understandable enough to
be acted upon. The new pkglint does this better.

The languages that are allowed in USE_LANGUAGES are defined differently
in the pkgsrc infrastructure, thus the old parsing code does not work
anymore. Therefore all identifiers are allowed now.

Dependency patterns like 'package>=1.0<2.0' are no longer marked as
wrong.

The debatable warning about plural names is gone.

The order of variables in simple Makefiles is no longer checked. Some new
variables have been added in the meantime, and keeping the consistent
order is not of utmost importance to those pkgsrc developers who work
with pkglint4. They are experienced enough to know the rules.

Missing manual pages are no longer marked in the PLIST files. It's not
the job of pkgsrc to provide these files.

The warning about unnoticed errors in pipelines like 'find | xargs' has
been removed because the shell parser is unreliable. This is solved
better in the new pkglint.