kernel: rename 'dumb' scheduler and simply call it 'simple'

Improve naming of the scheduler and call it what it is: simple. Using
'dumb' for the default scheduler algorithm in Zephyr is a bad idea.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

tests/kernel/sched/deadline/prj.conf

@@ -6,7 +6,7 @@ CONFIG_BT=n
 
 # Deadline is not compatible with MULTIQ, so we have to pick something
 # specific instead of using the board-level default.
-CONFIG_SCHED_DUMB=y
+CONFIG_SCHED_SIMPLE=y
 
 CONFIG_IRQ_OFFLOAD=y
 CONFIG_IRQ_OFFLOAD_NESTED=n

tests/kernel/sched/schedule_api/prj_simple.conf

@@ -1,7 +1,7 @@
 CONFIG_ZTEST=y
 CONFIG_IRQ_OFFLOAD=y
 CONFIG_TEST_USERSPACE=y
-CONFIG_SCHED_DUMB=y
+CONFIG_SCHED_SIMPLE=y
 CONFIG_MAX_THREAD_BYTES=6
 CONFIG_MP_MAX_NUM_CPUS=1
 CONFIG_ZTEST_FATAL_HOOK=y

tests/kernel/sched/schedule_api/testcase.yaml

@@ -29,11 +29,11 @@ tests:
     extra_args: CONF_FILE=prj_multiq.conf
     extra_configs:
       - CONFIG_TIMESLICING=n
-  kernel.scheduler.dumb_timeslicing:
-    extra_args: CONF_FILE=prj_dumb.conf
+  kernel.scheduler.simple_timeslicing:
+    extra_args: CONF_FILE=prj_simple.conf
     extra_configs:
       - CONFIG_TIMESLICING=y
-  kernel.scheduler.dumb_no_timeslicing:
-    extra_args: CONF_FILE=prj_dumb.conf
+  kernel.scheduler.simple_no_timeslicing:
+    extra_args: CONF_FILE=prj_simple.conf
     extra_configs:
       - CONFIG_TIMESLICING=n