undid last change to wxBitmapButton::GetBestSize(), in fact it doesn't make sense to support wxBU_EXACTFIT for it at all, so just removed the code doing it and mentioned it in the docs

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@30154 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/bbutton.tex

@@ -36,6 +36,10 @@ provided bitmaps. WIN32 only.}
 \twocolitem{\windowstyle{wxBU\_BOTTOM}}{Aligns the bitmap label to the bottom of the button. WIN32 only.}
 \end{twocollist}
 
+Note that \windowstyle{wxBU\_EXACTFIT} supported by 
+\helpref{wxButton}{wxbutton} is \emph{not} used by this class as bitmap buttons
+don't have any minimal standard size by default.
+
 See also \helpref{window styles overview}{windowstyles}.
 
 \wxheading{Event handling}