Revert "macOS: Improve deadkeys (#20515)" (#20570)

This reverts commit https://github.com/zed-industries/zed/pull/20515

I'm reverting for now to fix issues with key bindings on Nightly:
* `ctrl-c` and `ctrl-m` are being treated as `ctrl-enter`
* `ctrl-[` isn't working in vim mode
* there's a delay before `cmd-shift-[` switches tabs w/ vim mode enabled

Release Notes:

- N/A

crates/gpui/src/platform.rs

@@ -688,11 +688,6 @@ impl PlatformInputHandler {
             .flatten()
     }
 
-    #[allow(dead_code)]
-    fn apple_press_and_hold_enabled(&mut self) -> bool {
-        self.handler.apple_press_and_hold_enabled()
-    }
-
     pub(crate) fn dispatch_input(&mut self, input: &str, cx: &mut WindowContext) {
         self.handler.replace_text_in_range(None, input, cx);
     }
@@ -790,15 +785,6 @@ pub trait InputHandler: 'static {
         range_utf16: Range<usize>,
         cx: &mut WindowContext,
     ) -> Option<Bounds<Pixels>>;
-
-    /// Allows a given input context to opt into getting raw key repeats instead of
-    /// sending these to the platform.
-    /// TODO: Ideally we should be able to set ApplePressAndHoldEnabled in NSUserDefaults
-    /// (which is how iTerm does it) but it doesn't seem to work for me.
-    #[allow(dead_code)]
-    fn apple_press_and_hold_enabled(&mut self) -> bool {
-        true
-    }
 }
 
 /// The variables that can be configured when creating a new window