Remove unsupported colon from configure msg.

Remove unsupported colon from configure msg.

- When cross-compiling an answers file must be supplied via
  --cross-compile --cross-answers=<path to answers>.
- The lines in the answer file have the form;
    Config Msg: Answer
- The colon is used to delimit the msg and the answer when reading
  the answers file.
- WAF doesn't support the message containing a colon.
- It's not possible to override this variable so cross compile fails.

Signed-off-by: Zentaro Kavanagh <zentaro@google.com>
Reviewed-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>