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>

routers/web/user/setting/account_test.go

@@ -83,7 +83,7 @@ func TestChangePassword(t *testing.T) {
 		t.Run(req.OldPassword+"__"+req.NewPassword, func(t *testing.T) {
 			unittest.PrepareTestEnv(t)
 			setting.PasswordComplexity = req.PasswordComplexity
-			ctx := test.MockContext(t, "user/settings/security")
+			ctx, _ := test.MockContext(t, "user/settings/security")
 			test.LoadUser(t, ctx, 2)
 			test.LoadRepo(t, ctx, 1)