Remove unused <netinet/in_systm.h> and <resolv.h> inclusions.

[sortie]

netinet/in_systm.h defines n_short, n_long, and n_time which are not used anywhere in openssh.

resolv.h is not used in the affected files.

[djmdjm]

resolv.h is needed for base64 functions on some platforms

hostfile.c:97:8: error: call to undeclared function '__b64_pton'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        ret = __b64_pton(b64salt, salt, salt_len);