dashboard: remove MallocNanoZone environment variable workaround

We added a workaround in runtime/race on all supported versions
of Go (tip, 1.17, 1.16). This should not be necessary now.

Fixes golang/go#49940.
Updates golang/go#49138.

Change-Id: Idd337785571fa6f429435b31d22d34bf3b346ff2
Reviewed-on: https://go-review.googlesource.com/c/build/+/374334
Trust: Cherry Mui <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: cherrymui

dashboard/builders.go

@@ -579,7 +579,6 @@ var Hosts = map[string]*HostConfig{
 		Notes:     "MacStadium macOS Monterey (12.0) VM under VMWare ESXi",
 		env: []string{
 			"GOROOT_BOOTSTRAP=/Users/gopher/goboot", // Go 1.17.3
-			"MallocNanoZone=0",                      // golang.org/issue/49138
 		},
 		SSHUsername:     "gopher",
 		HermeticReverse: true, // we destroy the VM when done & let cmd/makemac recreate
@@ -599,7 +598,6 @@ var Hosts = map[string]*HostConfig{
 		Notes:     "macOS Big Sur (12.0) ARM64 (M1). Mac mini",
 		env: []string{
 			"GOROOT_BOOTSTRAP=/Users/gopher/goboot",
-			"MallocNanoZone=0", // golang.org/issue/49138
 		},
 		SSHUsername: "gopher",
 	},