Update api-conventions.md

Moved compatibility gotchas to api_changes.md

contributors/devel/api-conventions.md

@@ -1463,22 +1463,6 @@ be less than 256", "must be greater than or equal to 0".  Do not use words
 like "larger than", "bigger than", "more than", "higher than", etc.
 * When specifying numeric ranges, use inclusive ranges when possible.
 
-## Backward compatibility gotchas
-
-* A single feature/property cannot be represented using multiple spec fields in the same API version
-  simultaneously. Only one field can be populated in any resource at a time, and the client
-  needs to be able to specify which field they expect to use (typically via API version),
-  on both mutation and read. Old clients must continue to function properly while only manipulating
-  the old field. New clients must be able to function properly while only manipulating the new
-  field.
-* Changing any validation rules always has the potential of breaking some client, since it changes the
-  assumptions about part of the API, similar to adding new enum values. Validation rules on spec fields can
-  neither be relaxed nor strengthened. Strengthening cannot be permitted because any requests that previously
-  worked must continue to work. Weakening validation has the potential to break other consumers and generators
-  of the API resource. Status fields whose writers are under our control (e.g., written by non-pluggable
-  controllers), may potentially tighten validation, since that would cause a subset of previously valid
-  values to be observable by clients.
-
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