Remove support for changing magnification of active pane (#31981)

Closes #4265
Closes #24600

This setting causes many visual defects, and introduces unnecessary
(maintenance) complexity. as seen by #4265 and #24600


CC: @iamnbutler - How do you feel about this? I recommend looking at
https://github.com/zed-industries/zed/pull/24150#issuecomment-2866706506
for more context

Release Notes:

- Removed support

---------

Co-authored-by: Peter <peter@zed.dev>

crates/workspace/src/workspace_settings.rs

@@ -51,12 +51,6 @@ impl OnLastWindowClosed {
 #[derive(Copy, Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "snake_case")]
 pub struct ActivePanelModifiers {
-    /// Scale by which to zoom the active pane.
-    /// When set to 1.0, the active pane has the same size as others,
-    /// but when set to a larger value, the active pane takes up more space.
-    ///
-    /// Default: `1.0`
-    pub magnification: Option<f32>,
     /// Size of the border surrounding the active pane.
     /// When set to 0, the active pane doesn't have any border.
     /// The border is drawn inset.