patch 8.2.5171: dependencies and proto files are outdated

Problem:    Dependencies and proto files are outdated.
Solution:   Update dependencies and proto files.  Avoid errors.
diff --git a/src/proto/mbyte.pro b/src/proto/mbyte.pro
index 1cd02a9..c429adc 100644
--- a/src/proto/mbyte.pro
+++ b/src/proto/mbyte.pro
@@ -78,6 +78,7 @@
 int iconv_enabled(int verbose);
 void iconv_end(void);
 void f_getimstatus(typval_T *argvars, typval_T *rettv);
+void f_iconv(typval_T *argvars, typval_T *rettv);
 int convert_setup(vimconv_T *vcp, char_u *from, char_u *to);
 int convert_setup_ext(vimconv_T *vcp, char_u *from, int from_unicode_is_utf8, char_u *to, int to_unicode_is_utf8);
 int convert_input(char_u *ptr, int len, int maxlen);
@@ -86,5 +87,4 @@
 char_u *string_convert_ext(vimconv_T *vcp, char_u *ptr, int *lenp, int *unconvlenp);
 void f_setcellwidths(typval_T *argvars, typval_T *rettv);
 void f_charclass(typval_T *argvars, typval_T *rettv);
-void f_iconv(typval_T *argvars UNUSED, typval_T *rettv);
 /* vim: set ft=c : */