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 <[email protected]>

Author: mshawcroft

samples/net/echo_server/prj_frdm_k64f.conf

@@ -16,7 +16,6 @@ CONFIG_NET_IF_UNICAST_IPV4_ADDR_COUNT=1
 CONFIG_NET_MAX_CONTEXTS=10
 
 CONFIG_INIT_STACKS=y
-CONFIG_TEST_RANDOM_GENERATOR=y
 CONFIG_SYS_LOG_SHOW_COLOR=y
 CONFIG_PRINTK=y