remove unused patch; update test command and requirements

[bnavigator]

As discussed in python-control/Slycot#98 (comment)

I am not very familiar with the conda-forge and smithy workflow, but let's try:

Checklist

• Used a fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• @conda-forge-admin, please rerender
• Ensured the license file is being packaged.

Fixes #25

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[bnavigator]

Windows, Python 3.8:

================================== FAILURES ===================================
____________________________ test_xerbla_override _____________________________

    def test_xerbla_override():
        """Test that Fortran routines calling XERBLA do not print to stdout."""
    
        try:
            out = subprocess.check_output([sys.executable, '-c', CODE],
                                           stderr=subprocess.STDOUT,
                                           universal_newlines=True)
        except subprocess.CalledProcessError as cpe:
            raise RuntimeError("Trying to call _wrapper.ab08nd() failed with "
                               "returncode {}.\n"
                               "Captured STDOUT: \n {}\n"
                               "Captured STDERR: \n {}\n"
                               "".format(cpe.returncode, cpe.stdout, cpe.stderr))
    
        outlines = out.splitlines()
        assert len(outlines) == 2
>       assert outlines[0] == _wrapper.__file__
E       AssertionError: assert 'D:\\bld\\sly...win_amd64.pyd' == 'D:\\bld\\sly...win_amd64.pyd'
E         Skipping 42 identical trailing characters in diff, use -v to show
E         - %PREFIX%\Lib\site-p
E         ?                                       ^
E         + %PREFIX%\lib\site-p
E         ?                                       ^

Welcome to the world of case-insensitive path names 🤦

Going to fix this by skipping the test until we fix it in the Slycot source.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I wanted to let you know that I linted all conda-recipes in your PR (recipe) and found some lint.

Here's what I've got...

For recipe:

• Selectors are suggested to take a <two spaces>#<one space>[<expression>] form. See lines [39]

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[moorepants]

LGMT!