setuptools3.bbclass: clean up

setuptools3.bbclass: clean up

There's been a lot of work in this class lately, so a little spring
cleaning is needed.

Create wheels verbosely to help debug problems.

Remove unused SETUPTOOLS_INSTALL_ARGS, these can't be passed to
bdist_wheel.

Remove duplicate manipulation of files in bindir as pip_install_wheel
does the same.

Remove obsolete deletion of easy-install.pth, wheels don't generate that.

Remove obsolete ${datadir}/share fixup, pip-installed wheels can't
generate that path combination.

Remove purging of ${D} references from *.py, these won't be written by
standard setuptools, and recipes can do it themselves to work around
specific issues if needed.

Remove obsolete vardepsexclude of MACHINE on do_install, as that variable
isn't referenced.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>