Remove !libtool everywhere as this is already enforced in makepkg.conf

PKGBUILD

@@ -15,7 +15,6 @@ url="http://www.libpng.org/pub/png/libpng.html"
 license=('custom')
 depends=('lib32-zlib' $_pkgbasename)
 makedepends=(gcc-multilib)
-options=('!libtool')
 source=("https://downloads.sourceforge.net/sourceforge/${_pkgbasename}/${_pkgbasename}-${pkgver}.tar.xz"{,.asc}
         "https://downloads.sourceforge.net/sourceforge/libpng-apng/libpng-${_apngver}-apng.patch.gz")
 sha512sums=('89407c5abc1623faaa3992fc1e4a62def671d9a7401108dfceee895d5f16fe7030090bea89b34a36d377d8e6a5d40046886991f663ce075d1a2d31bf9eaf3c51'