Hopefully fix weird bug for Intel Mac users (#5652)

I don't have a machine locally that can reproduce the issue in #5597 but
have been working with @paperlib over Discord to try to narrow down the
cause. My fix in #5625 didn't fix the problem, so I'm *really* hoping
this patch does.

The problem presents as any text that matches the default bg color not
being rendered, regardless of the cell's bg color. The best I can figure
is that either we have some sort of accidental UB or there's a driver
bug (perhaps related to the addition of the `[[flat]]` interpolation
qualifier to the vertex out structure?), but I don't have a system
locally to iterate on to narrow it down.

src/renderer/shaders/cell.metal

@@ -487,13 +487,6 @@ vertex CellTextVertexOut cell_text_vertex(
     );
   }
 
-  // Don't bother rendering if the bg and fg colors are identical, just return
-  // the same point which will be culled because it makes the quad zero sized.
-  // However, we should still render if this is the cursor position
-  if (all(out.color == out.bg_color) && !is_cursor_pos) {
-    out.position = float4(0.0);
-  }
-
   return out;
 }