UI: Don't left align operator buttons in toolbars

This hack would make operator (push down) buttons without icons align
their text to the left in toolbars. Everywhere else in Blender, we
center it by default.

We barely use operator buttons in toolbars anymore. Even if we do and
there's a good reason to make text left aligned, it's better to use
`uiLayout.alignment = 'LEFT'` to achieve the same effect, but without
lowish-level hacks for a specific region type.

Differential Revision: https://developer.blender.org/D5527

source/blender/editors/interface/interface_layout.c

@@ -1180,11 +1180,6 @@ static uiBut *uiItemFullO_ptr_ex(uiLayout *layout,
 
   assert(but->optype != NULL);
 
-  /* text alignment for toolbar buttons */
-  if ((layout->root->type == UI_LAYOUT_TOOLBAR) && !icon) {
-    but->drawflag |= UI_BUT_TEXT_LEFT;
-  }
-
   if (flag & UI_ITEM_R_NO_BG) {
     layout->emboss = prev_emboss;
   }