Commit b7eda3e0e3 moves XidINMVCCSnapshot into snapmgr.{c,h},
however, it forgets the declaration of XidINMVCCSnapshot in
heapam.h.
Attached removes the redundant declaration in heapam.h.
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Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.