Revert "gpui: Assert validity of text runs for StyleText" (#39708)

Reverts zed-industries/zed#39581

This has done its job uncovering incorrect constructions of the
highlight ranges pretty fast. Reverting this to prevent this from
spilling into preview until I can fix the call sites next week

crates/gpui/src/text_system/line_wrapper.rs

@@ -225,15 +225,19 @@ impl LineWrapper {
 
 fn update_runs_after_truncation(result: &str, ellipsis: &str, runs: &mut Vec<TextRun>) {
     let mut truncate_at = result.len() - ellipsis.len();
+    let mut run_end = None;
     for (run_index, run) in runs.iter_mut().enumerate() {
         if run.len <= truncate_at {
             truncate_at -= run.len;
         } else {
             run.len = truncate_at + ellipsis.len();
-            runs.truncate(run_index + 1);
+            run_end = Some(run_index + 1);
             break;
         }
     }
+    if let Some(run_end) = run_end {
+        runs.truncate(run_end);
+    }
 }
 
 /// A fragment of a line that can be wrapped.