timesyncd: move stuff that is not about setting the clock out of manager_adjust_clock()

timesyncd: move stuff that is not about setting the clock out of manager_adjust_clock()

Let's make sure manager_adjust_clock() is purely about setting the
clock, and nothing else.

Let's clean up logging this way. manager_adjust_clock() now won#t log
about errors, but the caller can safely do that, and do with the right
log message string.