Remove cocoa.callbacks since nothing uses it

basis/cocoa/callbacks/authors.txt

@@ -1 +0,0 @@
-Kevin P. Reid

basis/cocoa/callbacks/callbacks.factor

@@ -1,33 +0,0 @@
-! Copyright (C) 2005, 2006 Kevin Reid.
-! See http://factorcode.org/license.txt for BSD license.
-USING: alien.c-types assocs kernel namespaces cocoa
-cocoa.classes cocoa.runtime cocoa.subclassing debugger ;
-IN: cocoa.callbacks
-
-SYMBOL: callbacks
-
-: reset-callbacks ( -- )
-    H{ } clone callbacks set-global ;
-
-reset-callbacks
-
-CLASS: {
-    { +name+ "FactorCallback" }
-    { +superclass+ "NSObject" }
-}
-
-{ "perform:" void { id SEL id }
-    [ 2drop callbacks get at try ]
-}
-
-{ "dealloc" void { id SEL }
-    [
-        drop
-        dup callbacks get delete-at
-        SUPER-> dealloc
-    ]
-} ;
-
-: <FactorCallback> ( quot -- id )
-    FactorCallback -> alloc -> init
-    [ callbacks get set-at ] keep ;

basis/cocoa/callbacks/platforms.txt

@@ -1 +0,0 @@
-macosx

basis/cocoa/callbacks/summary.txt

@@ -1 +0,0 @@
-Allows you to use Factor quotations as Cocoa actions