efi_loader: remove redundant hash includes

Remove the redundant includes of u-boot/sha1.h, u-boot/sha256.h
and u-boot/sha512.h

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>