Remove 'vm.panic_on_oom=1' (#7678)

#### Why I did it
If a process limits using nodes by mempolicy/cpusets, and those nodes become memory exhaustion status, one process may be killed by oom-killer.
No panic occurs in this case, because other node's memory may be free.
This means system total status may be not fatal yet.

#### How I did it
Remove 'vm.panic_on_oom=1' kernel flag from 'vmcore-sysctl.conf '

files/image_config/kdump/vmcore-sysctl.conf

@@ -4,4 +4,3 @@ kernel.panic_on_io_nmi=1
 kernel.panic_on_stackoverflow=1
 kernel.hung_task_panic=1
 kernel.unknown_nmi_panic=1
-vm.panic_on_oom=1