efi_loader: remove efi_delete_handle on loadfile2

Loadfile2 code is installing two protocols on it's own handle
and uses efi_delete_handle() to clean it up on failure(s). However
commit 05c4c9e2 ("efi_loader: define internal implementations of
install/uninstallmultiple") prepares the ground for us to clean up
efi_delete_handle() used in favor of Install/UninstallMultipleProtocol.

While at it clean up the non needed void casts to (void *) on the
protolcol installation.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>