package/python-ipython: bump to version 7.4.0

package/python-ipython: bump to version 7.4.0

- Update hash for COPYING.rst, it has been updated to remove
  BSD-3-Clause text:
  https://github.com/ipython/ipython/commit/5a6ef3e35db9ac04bf47a17d96484e03370f03dd
- Add LICENSE to license files as this is now the file that contain
  BSD-3-Clause text
- Needs python3 since version 6.x and above
- Needs new runtime dependencies: backcall and jedi
- Drop obsolete python2 dependencies as well as simplegeneric:
  https://github.com/ipython/ipython/commit/dc0ceb16f92e0e943435106e863a5cfccd724a2d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>