Revert "enable proxy for remaining clients (#152)"

This reverts commit 293835e.

It's unnecessary to specify ProxyFromEnvironment in these cases.
It was required for the selfhosted client, as we are overriding the
default Transport object.

In these cases, Transport are nil, and so should default to
DefaultTransport: https://cs.opensource.google/go/go/+/refs/tags/go1.22.0:src/net/http/client.go;l=60

This already has ProxyFromEnvironment as the default behaviour:
https://github.com/golang/go/blob/master/src/net/http/transport.go#L44

As this is unnecessary, it's better to leave it undefined to ensure that
the other characteristics of DefaultTransport are retained.

pkg/client/acr/acr.go

@@ -55,8 +55,7 @@ type ACRManifestResponse struct {
 
 func New(opts Options) (*Client, error) {
 	client := &http.Client{
-		Timeout:   time.Second * 5,
-		Transport: &http.Transport{Proxy: http.ProxyFromEnvironment},
+		Timeout: time.Second * 5,
 	}
 
 	if len(opts.RefreshToken) > 0 &&

pkg/client/docker/docker.go

@@ -52,8 +52,7 @@ type Image struct {
 
 func New(ctx context.Context, opts Options) (*Client, error) {
 	client := &http.Client{
-		Timeout:   time.Second * 10,
-		Transport: &http.Transport{Proxy: http.ProxyFromEnvironment},
+		Timeout: time.Second * 10,
 	}
 
 	// Setup Auth if username and password used.

pkg/client/ecr/ecr.go

@@ -3,7 +3,6 @@ package ecr
 import (
 	"context"
 	"fmt"
-	"net/http"
 	"sync"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -103,8 +102,6 @@ func (c *Client) getClient(region string) (*ecr.ECR, error) {
 			return nil, err
 		}
 	}
-	// Try and use an HTTP(S) Proxies defined within Environment variables.
-	client.Config.WithHTTPClient(&http.Client{Transport: &http.Transport{Proxy: http.ProxyFromEnvironment}})
 
 	c.cachedRegionClients[region] = client
 	return client, nil

pkg/client/gcr/gcr.go

@@ -35,14 +35,11 @@ type ManifestItem struct {
 }
 
 func New(opts Options) *Client {
-	client := &http.Client{
-		Timeout:   time.Second * 5,
-		Transport: &http.Transport{Proxy: http.ProxyFromEnvironment},
-	}
-
 	return &Client{
 		Options: opts,
-		Client:  client,
+		Client: &http.Client{
+			Timeout: time.Second * 5,
+		},
 	}
 }
 

pkg/client/ghcr/ghcr.go

@@ -25,8 +25,7 @@ func New(opts Options) *Client {
 	return &Client{
 		Options: opts,
 		Client: &http.Client{
-			Timeout:   time.Second * 5,
-			Transport: &http.Transport{Proxy: http.ProxyFromEnvironment},
+			Timeout: time.Second * 5,
 		},
 	}
 }

pkg/client/quay/quay.go

@@ -59,7 +59,6 @@ type responseManifestDataItem struct {
 
 func New(opts Options) *Client {
 	client := retryablehttp.NewClient()
-	client.HTTPClient.Transport = &http.Transport{Proxy: http.ProxyFromEnvironment}
 	client.RetryMax = 10
 	client.Logger = nil