Deprecation of "legacy" inline events

[SkymanOne]

Follow up for #1827 and related to #2031

Since the introduction of the shared event definition and the potential addition of the custom signature topic, it was realised that we need to maintain two sets of macros that serve identical purposes: legacy inline macros and new shared events.

Technically, the former can be achieved by the latter. Therefore, it is suggested to remove legacy inline events in favour of shared event definition. We have two ways of how to proceed:

1. Remove them now for the stable ink! 5.0.0 release
2. Keep them In 5.0.0, but add a deprecation notice and remove them in ink! 6.0.0. This would provide a smooth transition and time for the ecosystem to update docs and examples.
3. Keep inline events and maintain them alongside shared event definition

[ascjones]

For 2. we don't need to add the deprecation notice for 5.0, we can do it in a 5.x release.