echo_server: Remove unnecessary config from prf_frdm_k64f.conf

The k64f has a random driver the TEST_RANDOM_GENERATOR config is not
necessary.

Change-Id: I73bc4076cac459388d9dd9bf3eb89c8cb5ba7db7
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
1 file changed