Adjust profile_unload() definition to avoid clang 15 warning

With clang 15, the following -Werror warnings is produced:

sys/cddl/dev/profile/profile.c:640:15: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
profile_unload()
              ^
               void

This is because profile_unload() is declared with a (void) argument
list, but defined with an empty argument list. Make the definition match
the declaration.

MFC after: 3 days

(cherry picked from commit 2d03b58f9a3d5ec1deb35de594fcee22d06bfbb2)