[Sandbox service resolver hooks] Remove the RET hijacking in ntdll.

Changed the x64 ntdll hook to use JMP instead of RET.
(Also a quick fix to a DCHECK_NT with wrong logic.)

See bug ticket for x86/wow64 details (no changes needed).

BUG=510170
R=jschuh@chromium.org,wfh@chromium.org

Review URL: https://codereview.chromium.org/1504943002

Cr-Commit-Position: refs/heads/master@{#364220}
2 files changed