errors: move example functions into example_test file
Change-Id: Ide70476698d82a51881802dd6bf05dd7abcd60e8
GitHub-Last-Rev:
ddb251ded669d3dbbb96a05f4df7151c8d7c16d2
GitHub-Pull-Request: golang/go#57931
Reviewed-on: https://go-review.googlesource.com/c/go/+/462292
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>