remove uses of golang.org/x/sys/execabs

the "golang.org/x/sys/execabs" package was introduced to address a security
issue on Windows, and changing the default behavior of os/exec was considered
a breaking change. go1.19 applied the behavior that was previously implemented
in the execabs package;

from the release notes: https://go.dev/doc/go1.19#os-exec-path

> Command and LookPath no longer allow results from a PATH search to be found
> relative to the current directory. This removes a common source of security
> problems but may also break existing programs that depend on using, say,
> exec.Command("prog") to run a binary named prog (or, on Windows, prog.exe)
> in the current directory. See the os/exec package documentation for information
> about how best to update such programs.
>
> On Windows, Command and LookPath now respect the NoDefaultCurrentDirectoryInExePath
> environment variable, making it possible to disable the default implicit search
> of “.” in PATH lookups on Windows systems.

With those changes, we no longer need to use the execabs package, and we can
switch back to os/exec.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli-plugins/manager/candidate.go

@@ -1,8 +1,6 @@
 package manager
 
-import (
+import "os/exec"
-	exec "golang.org/x/sys/execabs"
-)
 
 // Candidate represents a possible plugin candidate, for mocking purposes
 type Candidate interface {

cli-plugins/manager/manager.go

@@ -3,6 +3,7 @@ package manager
 import (
 	"context"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -13,7 +14,6 @@ import (
 	"github.com/fvbommel/sortorder"
 	"github.com/spf13/cobra"
 	"golang.org/x/sync/errgroup"
-	exec "golang.org/x/sys/execabs"
 )
 
 // ReexecEnvvar is the name of an ennvar which is set to the command

cli/command/image/build/context.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"net/http"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -22,7 +23,6 @@ import (
 	"github.com/docker/docker/pkg/stringid"
 	"github.com/moby/patternmatcher"
 	"github.com/pkg/errors"
-	exec "golang.org/x/sys/execabs"
 )
 
 const (

cli/config/credentials/default_store.go

@@ -1,8 +1,6 @@
 package credentials
 
-import (
+import "os/exec"
-	exec "golang.org/x/sys/execabs"
-)
 
 // DetectDefaultStore return the default credentials store for the platform if
 // no user-defined store is passed, and the store executable is available.

cli/connhelper/commandconn/commandconn.go

@@ -20,6 +20,7 @@ import (
 	"io"
 	"net"
 	"os"
+	"os/exec"
 	"runtime"
 	"strings"
 	"sync"
@@ -28,7 +29,6 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
-	exec "golang.org/x/sys/execabs"
 )
 
 // New returns net.Conn