(bug 46431) Update Apple touch icon for en.wiktionary.

Changing the current Apple touch icon[1] into a new one[2]
per community request. I'm changing it only for en.wiktionary,
since the logos vary between the projects, and the current one
is set as default for all *.wiktionary.org projects.

Apple documentation at http://tiny.cc/frmpvw allows using
absolute URLs, not necessarily from within the domain itself,
so I'm doing just that (it's what we use for en.wikinews
already anyway).

There is also no need to have different sizes of the logo, as
iOS rescales it automatically; 144 x 144 is the suggested
size for Retina display.

== References ==
* (1) [[:commons:File:Wiktionary-iphone logo.png]];
* (2) [[:commons:File:Wiktionary-icon.png]];

Bug: 46431
Change-Id: I48c1774cb2bf3fa10b05b700a7ec3b50587de73a