extcon: palmas: Remove the mutually_exclusive array

This patch removes the mutually_exclusive array of extcon-palmas.c.
After used the unique id of each external connector on 2a9de9c0
("extcon: Use the unique id for external connector instead of string"),
extcon driver can't directly handle the bit value indicating the external
connectors.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>