Remove 'posting in the mailing list' in CONTRIBUTING.md (valkey-io#1174)

Remove reference to "the mailing list". We don't have a mailing list.

CONTRIBUTING.md

@@ -79,10 +79,9 @@ you need to ensure that the contribution is in accordance with the DCO.
 
 1. If it is a major feature or a semantical change, please don't start coding
 straight away: if your feature is not a conceptual fit you'll lose a lot of
-time writing the code without any reason. Start by posting in the mailing list
-and creating an issue at Github with the description of, exactly, what you want
-to accomplish and why. Use cases are important for features to be accepted.
-Here you can see if there is consensus about your idea.
+time writing the code without any reason. Start by creating an issue at Github with the
+description of, exactly, what you want to accomplish and why. Use cases are important for
+features to be accepted. Here you can see if there is consensus about your idea.
 
 2. If in step 1 you get an acknowledgment from the project leaders, use the following
 procedure to submit a patch: