Refactor web package and context package (#25298)

1. The "web" package shouldn't depends on "modules/context" package,
instead, let each "web context" register themselves to the "web"
package.
2. The old Init/Free doesn't make sense, so simplify it
* The ctx in "Init(ctx)" is never used, and shouldn't be used that way
* The "Free" is never called and shouldn't be called because the SSPI
instance is shared

---------

Co-authored-by: Giteabot <teabot@gitea.io>

services/repository/files/diff_test.go

@@ -17,7 +17,7 @@ import (
 
 func TestGetDiffPreview(t *testing.T) {
 	unittest.PrepareTestEnv(t)
-	ctx := test.MockContext(t, "user2/repo1")
+	ctx, _ := test.MockContext(t, "user2/repo1")
 	ctx.SetParams(":id", "1")
 	test.LoadRepo(t, ctx, 1)
 	test.LoadRepoCommit(t, ctx)
@@ -139,7 +139,7 @@ func TestGetDiffPreview(t *testing.T) {
 
 func TestGetDiffPreviewErrors(t *testing.T) {
 	unittest.PrepareTestEnv(t)
-	ctx := test.MockContext(t, "user2/repo1")
+	ctx, _ := test.MockContext(t, "user2/repo1")
 	ctx.SetParams(":id", "1")
 	test.LoadRepo(t, ctx, 1)
 	test.LoadRepoCommit(t, ctx)