[MLIR][Python] remove unused init python file (#104890)

remove unused `__init__.py` under `mlir/python/mlir/extras`
diff --git a/mlir/python/mlir/extras/__init__.py b/mlir/python/mlir/extras/__init__.py
deleted file mode 100644
index e69de29..0000000
--- a/mlir/python/mlir/extras/__init__.py
+++ /dev/null