Allow One-handed gesture when densityDpi > 600

This logic was aim to prevent tablet device enable One-handed gesture
so added displayInfo.densityDpi < DisplayMetrics.DENSITY_600 before.

However, it seems this densityDpi=600 does not able to represent to
tablet device, instead we already have system property
"ro.support_one_handed_mode" which provides feasibility to config false
on tablet project, as the reason we can safe to remove this condition.

Bug: 203936659
Test: adb shell wm density 600 , and observe OHM gesture is available
Test: atest WMShellUnitTests
Change-Id: Ic7ae10e8a47d26b9bb39ab80e22d591d74f89ae5
Merged-In: Ic7ae10e8a47d26b9bb39ab80e22d591d74f89ae5