efi_loader: return immediately in UCLASS_EFI_LOADER removal

In case of UCLASS_EFI_LOADER, EFI handles are managed by
EFI application/driver, we must not delete EFI handles.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>