input: touchscreen: remove dead code in it7258 driver

IT7258 touchscreen driver creates a character device which is
not used by anyone. Remove this dead code

Change-Id: Ied8a0048d8af17fa593c1970cabb572aac338786
Signed-off-by: Sudhakar Manapati <smanap@codeaurora.org>
Signed-off-by: Shantanu Jain <shjain@codeaurora.org>