Remove exportsfiles(["LICENSE"]).

The file doesn't exist, and using the exported target causes downstream errors.

For one, TensorFlow's license checker errors on these non-existing LICENSE files

PiperOrigin-RevId: 500257122

Author: pybind11_protobuf authors

pybind11_protobuf/BUILD

@@ -5,8 +5,6 @@ load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 
 licenses(["notice"])
 
-exports_files(["LICENSE"])
-
 pybind_library(
     name = "enum_type_caster",
     hdrs = ["enum_type_caster.h"],