Remove no longer applicable documentation from README.md.

ruby/README.md

@@ -7,74 +7,6 @@ we recommend using protoc's Ruby generation support with .proto files. The
 build process in this directory only installs the extension; you need to
 install protoc as well to have Ruby code generation functionality.
 
-JSON Migration Note
--------------------
-
-Users who were using the protobuf Gem `<= 3.0.0.alpha.5.0.4` will notice that
-the JSON format has changed slightly and is incompatible with previous
-versions.
-
-The change concerns field names.  Prior to the change, field names from the
-.proto file were used verbatim.  Take this `.proto` file:
-
-```protobuf
-syntax = "proto3";
-
-message M {
-  int32 my_int_field = 1;
-  bool my_bool_field = 2;
-}
-```
-
-Serializing to JSON used to give you something like this:
-
-```json
-{"my_int_field":1, "my_bool_field":true}
-```
-
-However this format was not compatible with the proto3 JSON spec.  To be
-compliant with proto3 JSON, we need to camel-case the names:
-
-```json
-{"myIntField":1, "myBoolField":true}
-```
-
-Starting with `3.0.0.alpha.5.0.5`, this bug was fixed and we now produce the
-correct camelCased names.  However this may cause compatibility problems for
-JSON users who can't upgrade everything at the same time, or who store
-serialized JSON payloads.  To mitigate this and allow time for migration, the
-library currently recognizes two environment variables:
-
-  - `UPB_JSON_ACCEPT_LEGACY_FIELD_NAMES`: set this variable to instruct the
-    JSON parser that the old names should be accepted in addition to the new,
-    compliant ones.  This will make the parser compatible with both formats.
-  - `UPB_JSON_WRITE_LEGACY_FIELD_NAMES`: set this variable to instruct the
-    JSON serializer to encode the old, non-compliant names.
-
-These options will be removed in a future version of Ruby protobuf.  All
-users shoud migrate to the standard names.
-
-If users have existing payloads in the old format and cannot easily migrate,
-the best solution would be to specify the old names explicitly in the
-`.proto` file using the `json_name` option.  For example, for the .proto
-file above, the user could specify:
-
-```protobuf
-syntax = "proto3";
-
-message M {
-  int32 my_int_field = 1 [json_name="my_int_field"];
-  bool my_bool_field = 2 [json_name="my_bool_field"];
-}
-```
-
-This will make all compliant proto3 JSON parsers/serializers use the
-non-camel-cased names forever.  Note that protobuf Ruby does *not yet*
-support this option properly, but support is forthcoming.  It will
-certainly be supported before the environment variables above are
-removed.
-
-
 Installation from Gem
 ---------------------