Optimizing: Do not insert suspend checks on back-edges.

Optimizing: Do not insert suspend checks on back-edges.

Rely on HGraph::SimplifyLoop() to insert suspend checks.

CodeGenerator's CheckLoopEntriesCanBeUsedForOsr() checks the
dex pcs of suspend checks against branch targets to verify
that we always have an appropriate point for OSR transition.
However, the HSuspendChecks that were added by HGraphBuilder
to support the recently removed "baseline" interfered with
this in a specific case, namely an infinite loop where the
back-branch jumps to a nop. In that case, the HSuspendCheck
added by HGraphBuilder had a dex pc different from the block
and the branch target but its presence would stop the
HGraph::SimplifyLoop() from adding a new HSuspendCheck with
the correct dex pc.

Bug: 27623547
Change-Id: I83566a260210bc05aea0c44509a39bb490aa7003