Temporarily remove visualization development docs. (elastic#58141)

docs/developer/visualize/development-visualize-index.asciidoc

@@ -1,21 +1,26 @@
 [[development-visualize-index]]
 == Developing Visualizations
 
-Kibana Visualizations are the easiest way to add additional functionality to Kibana. 
-This part of documentation is split into two parts. 
-The first part tells you all you need to know on how to embed existing Kibana Visualizations in your plugin. 
-The second step explains how to create your own custom visualization.
-
 [IMPORTANT]
 ==============================================
-These pages document internal APIs and are not guaranteed to be supported across future versions of Kibana. 
-However, these docs will be kept up-to-date to reflect the current implementation of Visualization plugins in Kibana.
+These pages document internal APIs and are not guaranteed to be supported across future versions of Kibana.
 ==============================================
 
-* <<development-embedding-visualizations>>
-* <<development-create-visualization>>
+The internal APIs for creating custom visualizations are in a state of heavy churn as
+they are being migrated to the new Kibana platform, and large refactorings have been
+happening across minor releases in the `7.x` series. In particular, in `7.5` and later
+we have made significant changes to the legacy APIs as we work to gradually replace them.
 
+As a result, starting in `7.5` we have removed the documentation for the legacy APIs
+to prevent confusion. We expect to be able to create new documentation later in `7.x`
+when the visualizations plugin has been completed.
 
-include::development-embedding-visualizations.asciidoc[]
+We would recommend waiting until later in `7.x` to upgrade your plugins if possible.
+If you would like to keep up with progress on the visualizations plugin in the meantime,
+here are a few resources:
 
-include::development-create-visualization.asciidoc[]
+* The <<breaking-changes,breaking changes>> documentation, where we try to capture any changes to the APIs as they occur across minors.
+* link:https://github.com/elastic/kibana/issues/44121[Meta issue] which is tracking the move of the plugin to the new Kibana platform
+* Our link:https://www.elastic.co/blog/join-our-elastic-stack-workspace-on-slack[Elastic Stack workspace on Slack].
+* The {repo}blob/{branch}/src/plugins/visualizations[source code], which will continue to be
+the most accurate source of information.

docs/visualize/aggregations.asciidoc

@@ -58,8 +58,6 @@ You can also nest these aggregations. For example, if you want to produce a thir
 
 {ref}/search-aggregations-pipeline-serialdiff-aggregation.html[Serial diff]:: Values in a time series are subtracted from itself at different time lags or periods.
 
-Custom {kib} plugins can <<development-visualize-index, add more capabilities to the default editor>>, which includes support for adding more aggregations.
-
 [float]
 [[visualize-sibling-pipeline-aggregations]]
 === Sibling pipeline aggregations