Drop Python minor versions from programming language list

There will often be new minor versions and they mostly do not affect
git-imerge, so listing them all is an unnecessary maintenance burden.

Author: pabs3

setup.py

@@ -42,14 +42,7 @@
         "License :: OSI Approved :: GNU General Public License v2 or later (GPLv2+)",
         "Programming Language :: Python",
         "Programming Language :: Python :: 2",
-        "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.4",
-        "Programming Language :: Python :: 3.5",
-        "Programming Language :: Python :: 3.6",
-        "Programming Language :: Python :: 3.7",
-        "Programming Language :: Python :: 3.8",
-        "Programming Language :: Python :: 3.9",
         "Environment :: Console",
         "Intended Audience :: Developers",
         "Topic :: Software Development :: Version Control :: Git",