Fix -Werror=duplicate-decl-specifier compilation issues

Fix -Werror=duplicate-decl-specifier compilation issues

capability.c:82:28: error: duplicate "const" declaration specifier
capability.c:110:33: error: duplicate "const" declaration specifier
rt_tgsigqueueinfo.c:42:61: error: duplicate "const" declaration specifier
utime.c:66:23: error: duplicate "const" declaration specifier
waitid.c:147:20: error: duplicate "const" declaration specifier

* capability.c (cap_user_header_t, cap_user_data_t): Remove.
(get_cap_header): Change return type
to "const struct user_cap_header_struct *".
(print_cap_header, print_cap_data): Change the type of last argument
to "const struct user_cap_header_struct * const".
(SYS_FUNC(capget)): Change type of "h" variable
to "const struct user_cap_header_struct *".
(SYS_FUNC(capset)): Change type of "h" variable
to "const struct user_cap_header_struct * const".
* tests/rt_tgsigqueueinfo.c (k_tgsigqueueinfo): Change the type of last
argument to "const void *const".
* tests/utime.c (main): Change the type of "tail_u" variable
to "const struct utimbuf *const".
* tests/waitid.c (do_waitid): Change the type of 3rd argument
to "const siginfo_t *const".