input: synaptics: remove outdated header

Remove the inclusion of the outdated (and now unused) asm/system.h.

This patch is propagated from msm-3.10 kernel
(commit: 720dd9b85ad6fe67e01ce3ecba84cc0a46b6b3bb
input: synaptics: remove outdated header)

Change-Id: Ic2081c61f4596d74560e00ffb4d486f7519ef473
Acked-by: Christian Bolis <cbolis@qti.qualcomm.com>
Signed-off-by: Keith Fallows <keithf@codeaurora.org>
Signed-off-by: Sudhakar Manapati <smanap@codeaurora.org>