setup.cfg: migrate some options off of pbr

setuptools natively supports declarative setup.cfg for a long time now, so there's no need to
specify this in pbr when it can be done in a more stock manner

setup.cfg

@@ -1,7 +1,8 @@
 [metadata]
 name = guake
 summary = Guake Terminal
-description_file = README.rst
+long_description = file: README.rst
+long_description_content_type = text/x-rst
 license_file = COPYING
 author = Gaetan Semet
 author_email = gaetan@xeberon.net
@@ -18,14 +19,15 @@ classifier =
     Topic :: Terminals :: Terminal Emulators/X Terminals
     Topic :: Desktop Environment :: Gnome
 
-[files]
+[options]
 packages =
     guake
 
+[files]
 data_files =
     share/guake/po = po/*
 
-[entry_points]
+[options.entry_points]
 console_scripts =
     guake = guake.main:exec_main
     guake-toggle = guake.guake_toggle:toggle_guake_by_dbus