runtime, cmd/go: roll back stale message, test detail

runtime, cmd/go: roll back stale message, test detail

Some debugging code was recently added to:
1) provide more detail for the stale reason when it is
determined that a package is stale
2) provide file and package time and date information when
it is determined that runtime.a is stale

This backs out those those debugging messages.

Fixes #19116

Change-Id: I8dd0cbe29324820275b481d8bbb78ff2c5fbc362
Reviewed-on: https://go-review.googlesource.com/37382
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>