patch 8.2.0183: tests fail when the float feature is disabled

Problem:    Tests fail when the float feature is disabled.
Solution:   Skip tests that don't work without float support.
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index e3f2c10..0fcc495 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -615,9 +615,8 @@
 endfunc
 
 func Test_writedelay()
-  if !has('reltime')
-    return
-  endif
+  CheckFunction reltimefloat
+
   new
   call setline(1, 'empty')
   redraw