authhandler: Remove example_test.go
authhandler: Remove example_test.go

The example test implementation uses stdin, which does not work in all environments:
https://github.com/golang/go/issues/45523

Removing for now to unblock release.

Change-Id: I49bafa9fe1d973b7c1d7ce00f51f110f9aa4a5a6
GitHub-Last-Rev: baf46329c243ccbe87cc822baaac86f71f45682c
GitHub-Pull-Request: golang/oauth2#488
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/309469
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Trust: Cody Oss <f11fa1e55ff5638510f5bf86ea76672a630250f9@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/oauth2