Clarify requirements for publication in ext dir

I removed this sentence because I don't think it's accurate.

We have these review criteria:
https://docs.civicrm.org/extensions/lifecycle/#review-criteria

The criteria do say that you can't use PHP overrides. But there are
other interfaces (like BAO functions for example) that are not in the
"supported methods" list but also not prohibited based on the extension
review criteria.

docs/extensions/index.md

@@ -54,7 +54,7 @@ Extensions which undergo a [formal review](/extensions/lifecycle.md#formal-revie
 
 ## Interacting with core
 
-There are a number of ways in which extensions can interact with core. These are supported to greater or lesser degrees and only extensions that use fully supported methods are eligible for publication in the extensions directory.
+There are a number of ways in which extensions can interact with core. These are supported to greater or lesser degrees.
 
 Fully supported methods are: