um: Remove CONFIG_FRAME_WARN from x86_64_defconfig

The CONFIG_FRAME_WARN=1024 setting in x86_64_defconfig originates
from arch/um/defconfig, which was split into i386_defconfig and
x86_64_defconfig by commit e40f04d040c6 ("arch/um: make it work
with defconfig and x86_64"). Currently, it's even smaller than the
default on 32bit (i.e., 1280). It's no longer suitable for 64bit.
Building with x86_64_defconfig triggers the following warning:

lib/maple_tree.c: In function ‘mas_wr_bnode’:
lib/maple_tree.c:3740:1: warning: the frame size of 1056 bytes is larger than 1024 bytes [-Wframe-larger-than=]
3740 | }
| ^

Since we have a larger CONFIG_KERNEL_STACK_ORDER on 64bit (twice
that of 32bit) by default, we could increase CONFIG_FRAME_WARN
accordingly. Let's remove the CONFIG_FRAME_WARN=1024 setting from
x86_64_defconfig and just use the default value (2048 for 64bit)
defined in lib/Kconfig.debug, as we do for 32bit.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260308060406.2772832-1-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>