libiconv-full: drop patch-libtool fixup

libiconv-full: drop patch-libtool fixup

It seems that this was required many years ago (It was added in 2012),
probably due to relying on outdated or broken libtool versions, but 1.17
uses libtool 2.4.7.

After trying building both host and target libiconv versions on Fedora and
MacOS I cannot seem to find what patch-libtool is supposed to fixup.

So, I can only presume that it is completely uneeded these days and can
be dropped.

Link: https://github.com/openwrt/openwrt/pull/18698
Signed-off-by: Robert Marko <[email protected]>