h8300: Fix <asm/tlb.h>

Ten years ago, a mismerge happened, concatenating two slightly different
versions of the same file. As a consequence, <asm-generic/tlb.h> was never
included, leading to a build failure only now:

kernel/cpu/idle.c: In function 'cpu_idle_loop':
kernel/cpu/idle.c:70:4: error: implicit declaration of function 'check_pgt_cache' [-Werror=implicit-function-declaration]

Remove the duplicates, and the header comment with the no longer correct
file name.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Yoshinori Sato <ysato@users.sourceforge.jp>