Revert "staging: android: ion: fix sys heap pool's gfp_flags"

This reverts commit acdaa51a.

This is a preparation change for merging android-4.14 commit
8ed9bc6e into msm-4.14 branch.
The reverted delta is committed already via:

9ca0b121 ion: add ion changes from msm-4.9 into msm-next

Change-Id: I1da3b8ac1ab5928d81e8192cc4567a1808c4a2ce
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>