Input: adp5589-keys - remove setup/teardown hooks for gpios

Input: adp5589-keys - remove setup/teardown hooks for gpios

This is currently just dead code. It's from around a time when
platform-data was used, and a board could hook it's own special callback
for setup/teardown, and a private object (via 'context').

This change removes it, as there are no more users in mainline for this.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20201112074308.71351-4-alexandru.ardelean@analog.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>