Back out "[TensorExpr] PyBind: bind ExternalCalls."
Summary: Original commit changeset: e1ea3b3630d1
Test Plan: Broke tests, e.g. T85754010
Reviewed By: ZolotukhinM
Differential Revision: D26727166
fbshipit-source-id: 42d2090bc55ec2982a4a08c38278c80617d5398a
