Do not check the return value of para_printf().

This function rarely fails, and if it does, we don't care too much. On
the other hand, checking the return value of each call to para_printf()
clutters the code considerably, especially in the error paths where
there is already an error code we have to keep.

This commit simply removes all error checking for para_printf(),
resulting in code which is easier to follow and less error-prone.