sanity.bbclass: do not check for presence of distutils

This will be removed in 3.12 and has been deprecated for a while.

If anything breaks because of its absence on the host, this would
expose the breakage so it can be fixed.

icu source specifically does not refer to distutils anywhere.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>