input: touchscreen: remove PRESSURE event from ft5x06 driver

There is no need to send ABS_MT_PRESSURE event when contact is
removed from touchscreen, this redundant event will confuse some
APP and cause malfunction.

CRs-Fixed: 537993
Change-Id: Ie2aef79f99cb80c10706f832cfab583ba742fdf1
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>