server: remove remaining crust from dropped eCos code

server: remove remaining crust from dropped eCos code

Commit 39650e2273bc ("ecosboard: delete bit-rotted eCos code") has
removed eCos code but has left some empty function that was used
during non-eCos build to replace eCos mutex.

Drop the functions and the file that contain them.

Change-Id: I31bc0237ea699c11bd70921660f960ee406ffa80
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6835
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>