Keep the LICENSE.txt file in lib/pythonX.Y dir

The license() builtin tries to read it and virtualenv tries to copy it.

See pypa/virtualenv#1352

Up until now, the license() builtin juts felt back to:

    See https://www.python.org/psf/license/

However it should output the full license text.

Virtualenv ~16.6 warns:

    No LICENSE.txt / LICENSE found in source

Technically, it is probably possible to install the package without
%license files, but that would simply resort to the previous noncritical
behavior.

This fix is not critical and hence it doesn't bump release, for easier
backporting to all our Python packages.

python3.spec

@@ -925,9 +925,6 @@ find %{buildroot} -name \*.bat -exec rm {} \;
 find %{buildroot}/ -name "*~" -exec rm -f {} \;
 find . -name "*~" -exec rm -f {} \;
 
-# Get rid of a stray copy of the license:
-rm %{buildroot}%{pylibdir}/LICENSE.txt
-
 # Do bytecompilation with the newly installed interpreter.
 # This is similar to the script in macros.pybytecompile
 # compile *.pyc
@@ -1075,7 +1072,6 @@ CheckPython optimized
 
 
 %files
-%license LICENSE
 %doc README.rst
 
 %if %{without flatpackage}
@@ -1098,13 +1094,14 @@ CheckPython optimized
 %{_mandir}/*/python.1*
 
 %files libs
-%license LICENSE
 %doc README.rst
 %endif
 
 %dir %{pylibdir}
 %dir %{dynload_dir}
 
+%license %{pylibdir}/LICENSE.txt
+
 %{pylibdir}/lib2to3
 %if %{without flatpackage}
 %exclude %{pylibdir}/lib2to3/tests