package/fetchmail: bump version to 6.4.0.beta5

package/fetchmail: bump version to 6.4.0.beta5

This bump brings buildroot in-line with Debian stable which also
provides this version after version 6.3 was removed from testing
in 2017: https://tracker.debian.org/pkg/fetchmail

Removed patches applied upstream:
https://gitlab.com/fetchmail/fetchmail/commit/bcab21a977732e2fe24f37cb394f913af0d8b166
https://gitlab.com/fetchmail/fetchmail/commit/a2ae6f8d15d7caf815d7bdd13df833fd1b2af5cc

fetchmailconf.py received various python3-related patches:
https://gitlab.com/fetchmail/fetchmail/commits/legacy_64/fetchmailconf.py

Therefore FETCHMAIL_REMOVE_FETCHMAILCONF_PY is not needed anymore.

Added license hash.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>