Remove 'OS Independent' trove classifier

We are not strictly OS independent anymore, since we access Linux
specific system functionality if it's available. The package does still
work on any system though.

Author: ruohola

pyproject.toml

@@ -24,7 +24,6 @@ classifiers = [
     "Intended Audience :: Developers",
     "Intended Audience :: Information Technology",
     "Intended Audience :: System Administrators",
-    "Operating System :: OS Independent",
     "Topic :: Internet :: WWW/HTTP",
     "Topic :: Internet :: WWW/HTTP :: WSGI :: Middleware",
     "Topic :: Software Development :: Libraries :: Python Modules",