Stop handling performKeyEquivalent: in wxOSX

We can't handle the accelerators (known as "key equivalents" in Cocoa)
in this function because it is called for the views in top to bottom
order, while wx semantics is for accelerators to be handled in the
accelerator table closest to the focused window.

So just remove this code and rely on accelerator handling happening in
wxWindowMac::OSXHandleKeyEvent() instead.

Closes #13937.

src/osx/cocoa/textctrl.mm

@@ -368,12 +368,6 @@ NSView* wxMacEditHelper::ms_viewCurrentlyEdited = nil;
         [super flagsChanged:event];
 }
 
-- (BOOL) performKeyEquivalent:(NSEvent*) event
-{
-    BOOL retval = [super performKeyEquivalent:event];
-    return retval;
-}
-
 - (void) insertText:(id) str
 {
     // We should never generate char events for the text being inserted