runsc: don't forward GOMAXPROCS environment variable to fsgofers

This is not strictly required for runsc-sandbox since
runsc/boot/loader.go:New() unconditionally overrides the default GOMAXPROCS via
a call to gomaxprocs.SetBase().

Alternatively, we could filter out the GOMAXPROCS environment variable from all
shim invocations of runsc (in e.g.
pkg/shim/v1/runsccmd/runsc.go:runsccmd.Runsc.command()). But since said
invocations of runsc run in containerd's cgroups and are thus subject to its
resource restrictions, it's not clear that this would be better.

PiperOrigin-RevId: 828079033

Author: nixprime

runsc/container/container.go

@@ -24,6 +24,7 @@ import (
 	"os/exec"
 	"path"
 	"regexp"
+	"slices"
 	"strconv"
 	"strings"
 	"syscall"
@@ -1309,6 +1310,10 @@ func (c *Container) createGoferProcess(conf *config.Config, mountHints *boot.Pod
 
 	// Start with the general config flags.
 	cmd := exec.Command(specutils.ExePath, conf.ToFlags()...)
+	// Don't forward GOMAXPROCS defaults that apply to this process (in
+	// particular, containerd-shim-runsc-v1 passes GOMAXPROCS=2 in
+	// v1.service.newCommand()).
+	cmd.Env = slices.DeleteFunc(os.Environ(), func(env string) bool { return strings.HasPrefix(env, "GOMAXPROCS=") })
 	cmd.SysProcAttr = &unix.SysProcAttr{
 		// Detach from session. Otherwise, signals sent to the foreground process
 		// will also be forwarded by this process, resulting in duplicate signals.