[0.4.9] cherry-pick [COMCTL32] Simplify some ifdefs CORE-14649

Addendum to 16d6c9b
Giannis suggested and Thomas explained:

Before the Wine sync, comctl32/button.c was based on ROS's
user32/button.c, so _USER32_ would highlight changes between
user32 (originally based on Wine) and comctl32. Now our
comctl32/button.c is based on Wine's comctl32/button.c, so
__REACTOS__ is enough.

(cherry picked from commit 1c151c9)

Author: JoachimHenze

dll/win32/comctl32/button.c

@@ -1177,7 +1177,7 @@ static UINT BUTTON_CalcLabelRect(const BUTTON_INFO *infoPtr, HDC hdc, RECT *rc)
    UINT        dtStyle = BUTTON_BStoDT( style, ex_style );
    RECT        r = *rc;
    INT         n;
-#if !defined(_USER32_) && defined(__REACTOS__)
+#ifdef __REACTOS__
     BOOL bHasIml = BUTTON_DrawIml(hdc, &infoPtr->imlData, &r, TRUE, 0);
 #endif
 
@@ -1229,7 +1229,7 @@ static UINT BUTTON_CalcLabelRect(const BUTTON_INFO *infoPtr, HDC hdc, RECT *rc)
 
       default:
       empty_rect:
-#if !defined(_USER32_) && defined(__REACTOS__)
+#ifdef __REACTOS__
          if (bHasIml)
              break;
 #endif
@@ -1238,7 +1238,7 @@ static UINT BUTTON_CalcLabelRect(const BUTTON_INFO *infoPtr, HDC hdc, RECT *rc)
          return (UINT)-1;
    }
 
-#if !defined(_USER32_) && defined(__REACTOS__)
+#ifdef __REACTOS__
    if (bHasIml)
    {
      if (infoPtr->imlData.uAlign == BUTTON_IMAGELIST_ALIGN_LEFT)
@@ -1322,7 +1322,7 @@ static void BUTTON_DrawLabel(const BUTTON_INFO *infoPtr, HDC hdc, UINT dtFlags,
     * I don't have Win31 on hand to verify that, so I leave it as is.
     */
 
-#if !defined(_USER32_) && defined(__REACTOS__)
+#ifdef __REACTOS__
     RECT rcText = *rc;
     BUTTON_DrawIml(hdc, &infoPtr->imlData, &rcText, FALSE, 0);
 #endif