xcode: Remove bitrotted Xcode project files

In Waffle's early days, some Mac OS contributors wanted to have their Xcode
project files tracked in git. It seemed odd to me, but maybe that's
standard practice for Xcode users. I dunno.

There was no harm in it, so I committed it... and forgot about it. Those
files have since bitrotted to hell, so this patch kills them.

As Emil points out, Xcode users should generate the project files with
`cmake -GXcode`.

Reported-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>