remove unnecessary "__provides_exclude_from" and custom definition of "python3_pkgversion"

"__provides_exclude_from" macro is unnecessary in Fedora and EPEL 7.
See [1] for detailed explanation.

All currently supported versions of Fedora provide "python3_pkgversion"
out of the box (it exists since Fedora 24 or 25) so we can remove the
extra line here.

[1] https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/K3NLDLK4XVARTSROC6XVKNVW72BMMHYE/

python-msgpack.spec

@@ -1,10 +1,5 @@
 %global srcname msgpack
 %global sum A Python MessagePack (de)serializer
-%global __provides_exclude_from ^(%{python2_sitearch}/.*\\.so)$
-%global __provides_exclude_from ^(%{python3_sitearch}/.*\\.so)$
-
-# For old Fedora versions
-%{!?python3_pkgversion:%global python3_pkgversion 3}
 
 Name:           python-%{srcname}
 Version:        0.5.6