input: synaptics_dsx: remove some sysfs nodes.

Remove most sysfs entrypoints to fw_update module.
Retains check_fw, which is triggered from an
init script.

BUG: 32769717
Change-Id: I710cb37a8b5382dce7aa6a1d8748be5853a18a7a
Signed-off-by: Andrew Chant <achant@google.com>