patch 9.0.0657: too many #ifdefs

Problem:    Too many #ifdefs.
Solution:   Graduate the +cmdwin feature.  Now the tiny and small builds are
            equal, drop the small build.  (Martin Tournoij, closes #11268)
diff --git a/src/window.c b/src/window.c
index ad1852e..52c458e 100644
--- a/src/window.c
+++ b/src/window.c
@@ -119,12 +119,8 @@
     win_T *
 prevwin_curwin(void)
 {
-    return
-#ifdef FEAT_CMDWIN
-	// In cmdwin, the alternative buffer should be used.
-	is_in_cmdwin() && prevwin != NULL ? prevwin :
-#endif
-	curwin;
+    // In cmdwin, the alternative buffer should be used.
+    return is_in_cmdwin() && prevwin != NULL ? prevwin : curwin;
 }
 
 /*
@@ -149,8 +145,7 @@
     if (ERROR_IF_ANY_POPUP_WINDOW)
 	return;
 
-#ifdef FEAT_CMDWIN
-# define CHECK_CMDWIN \
+#define CHECK_CMDWIN \
     do { \
 	if (cmdwin_type != 0) \
 	{ \
@@ -158,9 +153,6 @@
 	    return; \
 	} \
     } while (0)
-#else
-# define CHECK_CMDWIN do { /**/ } while (0)
-#endif
 
     Prenum1 = Prenum == 0 ? 1 : Prenum;
 
@@ -2963,10 +2955,9 @@
 {
     int		dummy;
 
-#ifdef FEAT_CMDWIN
     // avoid an error for switching tabpage with the cmdline window open
     cmdwin_type = 0;
-#endif
+
     while (first_tabpage->tp_next != NULL)
 	tabpage_close(TRUE);
 
@@ -4019,13 +4010,11 @@
     tabpage_T	*newtp;
     int		n;
 
-#ifdef FEAT_CMDWIN
     if (cmdwin_type != 0)
     {
 	emsg(_(e_invalid_in_cmdline_window));
 	return FAIL;
     }
-#endif
 
     newtp = alloc_tabpage();
     if (newtp == NULL)
@@ -5513,7 +5502,6 @@
 #endif
 }
 
-#if defined(FEAT_CMDWIN) || defined(PROTO)
 /*
  * Save the size of all windows in "gap".
  */
@@ -5567,7 +5555,6 @@
 	(void)win_comp_pos();
     }
 }
-#endif // FEAT_CMDWIN
 
 /*
  * Update the position for all windows, using the width and height of the
@@ -6419,10 +6406,9 @@
 
     if (wp->w_buffer->b_ml.ml_line_count < wp->w_height)
 	return;
-#ifdef FEAT_CMDWIN
     if (skip_win_fix_cursor)
 	return;
-#endif
+
     // Determine valid cursor range.
     so = MIN(wp->w_height / 2, so);
     wp->w_cursor.lnum = wp->w_topline;