runtime,hash/maphash: eliminate maphash torture test for -race

runtime,hash/maphash: eliminate maphash torture test for -race

Disable the "torture" portion of the maphash tests if -race is in
effect (these tests can cause timeouts on the longtest -race builder).

Fixes #57030.

Change-Id: I23d7561dac3e81d979cad9e0efa6f5b7154aadd2
Reviewed-on: https://go-review.googlesource.com/c/go/+/454455
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>