macros.python: drop last %__python2 occurrence

This is needed so people can do things like:

    %if %{with python3}
    %global __python %__python3
    %else
    %global __python %__python2
    %else

And than just use %__python, %py_build, %py_install,
%python_sitelib, ...

macros.python

@@ -5,7 +5,7 @@
 # the macro
 %py_build() %{expand:\\\
   CFLAGS="${CFLAGS:-${RPM_OPT_FLAGS}}" LDFLAGS="${LDFLAGS:-${RPM_LD_FLAGS}}"\\\
-  %{__python} %{py_setup} %{?py_setup_args} build --executable="%{__python2} %{py_shbang_opts}" %{?*}
+  %{__python} %{py_setup} %{?py_setup_args} build --executable="%{__python} %{py_shbang_opts}" %{?*}
   sleep 1
 }