These definitions are evidently left over from the days when
sparsemem settings were platform specific. This was no longer
the case when the platform got merged.

There was no warning in the past, but now the asm/sparsemem.h
header ends up being included indirectly, causing this warning:

In file included from /git/arm-soc/arch/arm/mach-keystone/keystone.c:24:
arch/arm/mach-keystone/memory.h:10:9: warning: 'SECTION_SIZE_BITS' macro redefined [-Wmacro-redefined]
 #define SECTION_SIZE_BITS       34
        ^
arch/arm/include/asm/sparsemem.h:23:9: note: previous definition is here
 #define SECTION_SIZE_BITS       28
        ^

Clearly the definitions never had any effect here, so remove them.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20201203231847.1484900-1-arnd@kernel.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>