Remove experimental_generate_mutable_types from fbsource

Summary:
Remove `experimental_generate_mutable_types` and `experimental_generate_abstract_types` from fbsource.
They are generated by default with "python" language.

Reviewed By: rmakheja

Differential Revision: D67422172

fbshipit-source-id: 5e4db189b1e4b5efa5d2c6ac8642e7a500bd9f6d

fb303/thrift/BUCK

@@ -46,11 +46,6 @@ thrift_library(
     thrift_cpp2_options = "frozen2,reflection",
     thrift_java_swift_options = ["deprecated_allow_leagcy_reflection_client"],
     thrift_js_options = ["node"],
-    # DO_BEFORE(aristidis, 20250130): Remove experimental flags after launch.
-    thrift_python_options = [
-        "experimental_generate_mutable_types",
-        "experimental_generate_abstract_types",
-    ],
     thrift_rust_options = [
         "deprecated_default_enum_min_i32",
         "serde",