package/supervisor: drop python-meld3 dependency

python-meld3 is not a dependency since bump to version 4.1.0 in commit
5da3e1a3 and
https://github.com/Supervisor/supervisor/commit/d09d843493eb77cb8c3df52e1f7e636ad0e5b4dd



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>