draw: Remove draw_install_aaline_stage dead code.

Remove dead code left over from commit dbb2cf38 ("draw: simplify (and correct) aaline fallback (v2)").

Fix defect reported by Coverity Scan.

Logically dead code (DEADCODE) dead_error_line: Execution cannot reach this statement: (*aaline->stage.destroy)(&a....

Signed-off-by: Vinson Lee vlee@freedesktop.org

cc: @sroland