Drop the deprecated pkg_resources dependency from setup.py.

pkg_resources was removed in setuptools 81+, breaking the build with the
"No module named 'pkg_resources'" error. It was only used to parse a trivial
requirements.txt, so replace it with plain line parsing.

Upstream: https://github.com/netinvent/command_runner

--- a/setup.py
+++ b/setup.py
@@ -14,7 +14,6 @@ PACKAGE_NAME = "command_runner"
 import sys
 import os

-import pkg_resources
 import setuptools


@@ -65,8 +64,9 @@ def parse_requirements(filename):
     try:
         requirements_txt = _read_file(filename)
         install_requires = [
-            str(requirement)
-            for requirement in pkg_resources.parse_requirements(requirements_txt)
+            line.strip()
+            for line in requirements_txt.splitlines()
+            if line.strip() and not line.strip().startswith("#")
         ]
         return install_requires
     except OSError: