[DOCS] Removes out-dated info from Watcher limitations

[lcawl]

This PR removes the following Watcher limitation from the documentation:

https://www.elastic.co/guide/en/elastic-stack-overview/master/watcher-limitations.html#_watcher_ui

There is no longer a "Save" button so this work-around no longer applies.

[elasticmachine]

Pinging @elastic/es-core-features

[elasticmachine]

Pinging @elastic/es-docs

[jakelandis]

The save button is still there, it is just called Create watch or Save watch and moved.

edit:

However, with out any history or context, this seems like an odd thing to call out in the first place.

I am +1 to accept this change as-is or +1 to update the image.

cc @elastic/es-ui

[alisonelizabeth]

++ to @jakelandis's comment.

FWIW I think this would apply to many of our apps, not just watcher, so it seems strange that we were only calling it out for watcher.

[cjcenizal]

I think we had good intentions when we originally added this documentation but I agree that it's incongruous with the rest of our content and removing it is for the best.

[jakelandis]

thanks @alisonelizabeth @cjcenizal

LGTM as-is to remove it (but may want to tweak the commit message).