common: remove bedbug debugger support

Commit 98f705c9 ("powerpc: remove 4xx support") removed (in 2017) the
last code that made use of bedbug debugger support. Since there aren't
any boards left that define either CONFIG_CMD_BEDBUG or a real
bedbug_init(), drop this feature from u-boot.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Simon Glass <sjg@chromium.org>