m68k: Remove M5271EVB and idmr board support

m68k: Remove M5271EVB and idmr board support

CONFIG_SYS_HZ must be always 1000, but M5271EVB.h defines it
as 1000000 and idmr.h defines it as (50000000 / 64).

When compiling these two boards, a warning message is displayed:

  time.c:14:2: warning: #warning "CONFIG_SYS_HZ must be 1000
  and should not be defined by platforms" [-Wcpp]

There are no board maintainers for them so this commit just
deletes them.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jason Jin <Jason.jin@freescale.com>