Fix CONTRIBUTING (#534)

CONTRIBUTING.md

@@ -56,37 +56,12 @@ The `make` compiles TypeScript to Javascript and runs all test cases
 (in `spec/`) in nodejs (using jasmine) and in a headless browser (using karma 
 and jasmine). 
 
-Some test cases use test fixtures from `packages/test-fixtures`. 
 
-
-##### Test fixtures
-
-`packages/test-fixtures/index.ts` exports a `FixtureRegistry`. This registry 
-provides access to a collection of message type fixtures. 
-
-A message type fixture is basically a set of test data for a specific protobuf 
-message. It has a type name (the qualified protobuf message type name) and 
-reflection field information. It can also provide message instances.   
-
-The only purpose of the fixtures is to isolate test data from test code to make 
-test cases more readable.
+##### Protos
 
-`packages/test-fixtures` also contains a large number of .proto files. These 
+`packages/proto` contains a large number of .proto files. These 
 files are used to test code generation and functionality of the generated code. 
 
-For each fixture, there should also be a corresponding .proto file. This makes 
-it possible to compare the field information generated by the plugin to the 
-field information in the fixture data, asserting that the plugin generates 
-expected data. 
-
-`packages/test-fixtures/all.descriptorset` is a binary protobuf message of type 
-`FileDescriptorSet` (defined in `google/protobuf/descriptor.proto`). It contains 
-file descriptors for all .proto files in `test-fixtures`. The descriptor set 
-is generated using protoc (see `packages/plugin/Makefile` and 
-`packages/plugin-framework/Makefile`). A `FileDescriptorSet` can be used to 
-run the plugin during testing without invoking protoc.
-
-
 ##### Testing the plugin
 
 All protobuf plugins work with `CodeGeneratorRequest` and `CodeGeneratorResponse`