Avoid adding region space bitmap to heap bitmap

Adding the bitmap here really served no purpose and caused
VisitObjects to visit region space bitmap objects twice. This had
unwanted results like adding objects to hprof dumps twice.

Regression test is covered by DCHECK in hprof and test 130.

Test: N6P boot and test-art-host

Bug: 34967844
Change-Id: I53a6075d577430089bb42f84a3c80c1cc5302206
2 files changed