docs: remove protobuf generation instructions

Author: vbarua

CONTRIBUTING.md

@@ -37,14 +37,6 @@ You can run the full code generation using the following command or use the indi
 pixi run codegen
 ```
 
-## Protobuf stubs
-
-Run the proto codegen only:
-
-```
-pixi run codegen-proto
-```
-
 ## Antlr grammar
 
 Substrait uses antlr grammar to derive output types of extension functions. Make sure java is installed and ANTLR_JAR environment variable is set. Take a look at .devcontainer/Dockerfile for example setup.

pyproject.toml

@@ -56,12 +56,10 @@ update-substrait = [ { task = "update-submodule" }, { task = "codegen" }]
 
 update-submodule = "./update_submodule.sh"
 
-codegen = [{ task = "antlr" }, { task = "codegen-proto" }, { task = "codegen-extensions" }]
+codegen = [{ task = "antlr" }, { task = "codegen-extensions" }]
 
 check-codegen = "./check_codegen.sh"
 
-codegen-proto = "./gen_proto.sh"
-
 antlr = """
 	cd third_party/substrait/grammar \
 		&& antlr4 -o ../../../src/substrait/gen/antlr -Dlanguage=Python3 SubstraitType.g4 \