Revert "drm/amdkfd: Add memory sync before TLB flush on unmap"

This reverts commit 3be4dca1.

Reason for revert: it causes regressions on several Asics.

Signed-off-by: Eric Huang <jinhuieric.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>