Remove warning if release is purple-listed

Changes introduced

In !1759 (merged) a check was introduced for purple-listed releases which consisted of :

1. throwing a warning in the using release field if the release was purple-listed in general
2. throwing a warning from the Pythia8 checks if the purple-list reason contained CKKW-L AND the jO actually used CKKW-L merging

From discussions in !1808 (merged) it looks like we only want to keep (2) and not throw a general warning if a release is purple-listed. Here I remove the 1st warning which should also fix the pipeline failing in !1808 (merged)

Tests

Before fix

After fix

Issues resolved

Closes #