Revert "Use scap library to implement screensharing on X11 (#27807)" (#28141)

This reverts commit c2afc2271b.

Build on ARM if failing, likely because `c_char` is `u8` on arm and `i8`
on x86:

```
error[E0308]: mismatched types
   --> /home/runner/.cargo/git/checkouts/scap-40ad33e1dd47aaea/5715067/src/targets/linux/mod.rs:75:74
    |
75  |     let result = unsafe { XmbTextPropertyToTextList(display, &mut xname, &mut list, &mut count) };
    |                           -------------------------                      ^^^^^^^^^ expected `*mut *mut *mut u8`, found `&mut *mut *mut i8`
    |                           |
    |                           arguments to this function are incorrect
    |
    = note:    expected raw pointer `*mut *mut *mut u8`
            found mutable reference `&mut *mut *mut i8`
note: function defined here
   --> /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/x11-2.21.0/src/xlib.rs:552:10
    |
552 |   pub fn XmbTextPropertyToTextList (_4: *mut Display, _3: *const XTextProperty, _2: *mut *mut *mut c_char, _1: *mut c_int) -> c_int,
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^
```

Release Notes:

- N/A

crates/gpui/src/platform/linux/platform.rs

@@ -28,7 +28,6 @@ use crate::{
     Pixels, Platform, PlatformDisplay, PlatformTextSystem, PlatformWindow, Point, Result,
     ScreenCaptureSource, Task, WindowAppearance, WindowParams, px,
 };
-
 #[cfg(any(feature = "wayland", feature = "x11"))]
 pub(crate) const SCROLL_LINES: f32 = 3.0;
 
@@ -51,10 +50,6 @@ pub trait LinuxClient {
     #[allow(unused)]
     fn display(&self, id: DisplayId) -> Option<Rc<dyn PlatformDisplay>>;
     fn primary_display(&self) -> Option<Rc<dyn PlatformDisplay>>;
-    fn is_screen_capture_supported(&self) -> bool;
-    fn screen_capture_sources(
-        &self,
-    ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>>;
 
     fn open_window(
         &self,
@@ -235,14 +230,12 @@ impl<P: LinuxClient + 'static> Platform for P {
         self.displays()
     }
 
-    fn is_screen_capture_supported(&self) -> bool {
-        self.is_screen_capture_supported()
-    }
-
     fn screen_capture_sources(
         &self,
     ) -> oneshot::Receiver<Result<Vec<Box<dyn ScreenCaptureSource>>>> {
-        self.screen_capture_sources()
+        let (mut tx, rx) = oneshot::channel();
+        tx.send(Err(anyhow!("screen capture not implemented"))).ok();
+        rx
     }
 
     fn active_window(&self) -> Option<AnyWindowHandle> {