target: remove handling of target's deprecated_name

target: remove handling of target's deprecated_name

We do not have anymore any deprecated target name.
Drop the code to handle deprecated target names and the placehold
in struct target_type.

This patch is separated from the patch that drops the remaining
deprecated target names to be ready to revert this if there is any
need in the future.

Change-Id: I96fca7ffa39d8292f81e79f115ea45c4a30035d7
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6087
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>