Revert "Support Go 1.13 error chains in `Cause` (pkg#215)" (pkg#220)

This reverts commit 49f8f61.

Support Go 1.13 error chains in `Cause` (pkg#215)

errors v0.8.1

release errors 0.8.0

release errors version 0.7.1

errors version 0.7.0

errors version 0.6.0

errors version 0.5.1

errors version 0.5.0

errors release 0.4.0