Commits 54489ba1672 and 67adc03ef8 replaced some isc_socket_sendto()
calls with isc_socket_sendto2() calls without taking into consideration
that the latter cannot fail due to lack of memory, leaving some
redundant code behind.

On Unix systems, isc_socket_sendto2() called with no flags set always
returns ISC_R_SUCCESS.

On Windows systems, isc_socket_sendto2() called with no flags set can
only return a value different than ISC_R_SUCCESS due to a programmatic
error (ISC_R_CONNREFUSED, when the socket is closed).

Thus, we should never really expect anything other than ISC_R_SUCCESS
from isc_socket_sendto2() called with flags == 0.  Attempts to handle
such situations are misleading, plus evaluating one such error handling
branch in resquery_send() (introduced for the right reasons in
146057d7e7) actually leads to a crash (since commit adbf81335b).