Delete codes for ethio-mode, which

Delete codes for ethio-mode, which
includes deletion of varialble ethio-mode, variable
ethio-mode-map, and function ethio-mode.
(exit-ethiopic-environment-data): New variable.
(setup-ethiopic-environment): Recode information of changed key
bindings in exit-ethiopic-environment-data.  Add
ethio-select-a-translation to quail-mode-hook.
(exit-ethiopic-environment): New function.
(ethio-find-file): Don't check ethio-mode.
(ethio-write-file): Likewise.