remove EXPORT_SYMBOL in header files

[dtcccc]

Currently, delete_export_symbol() only removes EXPORT_SYMBOL from mod_srcs (.c files), but ignores mod_hdrs (.h files).
In headers such as include/linux/bpf.h, EXPORT_SYMBOL still remains.

[chenshanpei]

#define DEFINE_BPF_DISPATCHER(name)                                     \
        noinline unsigned int bpf_dispatcher_##name##_func(             \
                const void *ctx,                                        \
                const struct bpf_insn *insnsi,                          \
                unsigned int (*bpf_func)(const void *,                  \
                                         const struct bpf_insn *))      \
        {                                                               \
                return bpf_func(ctx, insnsi);                           \
        }                                                               \
        EXPORT_SYMBOL(bpf_dispatcher_##name##_func);                    \
        struct bpf_dispatcher bpf_dispatcher_##name =                   \
                BPF_DISPATCHER_INIT(bpf_dispatcher_##name);