chore(AIP-215): change "PA" to "Organization". (#1101)

Author: shwoodard

aip/general/0215.md

@@ -47,18 +47,18 @@ benefit.
 
 ### What if a proto will never change?
 
-There are some situations where it is useful to have an unversioned proto.
-These should generally apply to a complete product area or suite of APIs, not
-just a single API. In these situations, it may be possible to add it to our
-collections of common protos. Common protos are able to be used by many APIs,
-and are always unversioned.
+There are some situations where it is useful to have an unversioned
+proto. These should generally apply to a complete organization or suite
+of APIs, not just a single API. In these situations, it may be possible
+to add it to our collections of common protos. Common protos are able to
+be used by many APIs, and are always unversioned.
 
 Common protos shall always have a package structure ending in `type` (e.g.
-`google.type`, `google.cloud.type`).
+`google.type` or `google.cloud.type`).
 
-**Warning:** This is a relatively rare occurrence. If you find yourself adding
-protos to your PA's `type` directory frequently, double-check that this is
-actually where they belong.
+**Warning:** This is a relatively rare occurrence. If you find yourself
+adding protos to your organizations's `type` directory frequently,
+double-check that this is actually where they belong.
 
 For more information on common protos, consult [AIP-213][].