When the flag package first begin printing nonzero defaults, the test
was against a fixed set of string representations of zero values.
This worked until the string representation of a time.Duration
changed from "0" to "0s", causing the zero Duration to register as
nonzero. The flag package then added reflect-based code that fell back
to the old test. This failed to work when a nonzero default for a flag
happened to be the string representation of one the original fixed set
of zero values in the original test. This change removes the original
test, allowing the reflect-based code to be the only deciding factor.

Fixes #23543

Change-Id: I582ce554d6729e336fdd96fb27340674c15350d8
Reviewed-on: https://go-review.googlesource.com/103867Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>