runtime: re-enable TestArenaCollision on darwin in race mode
runtime: re-enable TestArenaCollision on darwin in race mode

Go 1.14 will drop support for macOS 10.10, see #23011

This reverts CL 155097

Updates #26475
Updates #29340

Change-Id: I64d0275141407313b73068436ee81d13eacc4c76
Reviewed-on: https://go-review.googlesource.com/c/go/+/214058
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,golang/go,akutz/go,cloudflare/go,akutz/go,CAFxX/go,akutz/go,akutz/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,nawawi/go,golang/go,akutz/go,nawawi/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,akutz/go,CAFxX/go,golang/go