Remove 10.12 check handled by respondsToSelector

atom/browser/native_window_mac.mm

@@ -764,7 +764,6 @@ NativeWindowMac::NativeWindowMac(
     [window_ setOpaque:NO];
   }
 
-  if (base::mac::IsAtLeastOS10_12()) {
   // Create a tab only if tabbing identifier is specified and window has
   // a native title bar.
   if (tabbing_identifier_.empty() || transparent() || !has_frame()) {
@@ -776,7 +775,6 @@ NativeWindowMac::NativeWindowMac(
       [window_ setTabbingIdentifier:base::SysUTF8ToNSString(tabbing_identifier_)];
     }
   }
-  }
 
   // We will manage window's lifetime ourselves.
   [window_ setReleasedWhenClosed:NO];