fuzz: remove unnecessary internal headers from wasm_mutator_fuzz (#4865)

Remove `wasm_runtime_common.h` and `bh_read_file.h` includes from the
wasm_mutator_fuzz harness. All runtime APIs used by this fuzzer
(wasm_runtime_init, wasm_runtime_load, wasm_runtime_instantiate,
wasm_runtime_call_wasm_a, wasm_runtime_get_export_count, etc.) are
declared in the public `wasm_export.h` header.

- `wasm_runtime_common.h` (core/iwasm/common/) is an internal
  implementation header not intended for external use.
- `bh_read_file.h` (core/shared/utils/uncommon/) is an internal
  utility header whose functions are never called in this fuzzer.

Verified that the modified harness compiles and runs correctly for all
three build targets (classic-interp, fast-interp, llvm-jit) with
identical code coverage.

tests/fuzz/wasm-mutator-fuzz/wasm-mutator/wasm_mutator_fuzz.cc

@@ -1,9 +1,7 @@
 // Copyright (C) 2019 Intel Corporation. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include "wasm_runtime_common.h"
 #include "wasm_export.h"
-#include "bh_read_file.h"
 #include <stdlib.h>
 #include <stdio.h>
 #include <errno.h>