Make wxWS_EX_VALIDATE_RECURSIVELY default (and only) behaviour

In practice, almost everybody using validators also seems to use this style,
so make it the default (this hadn't been done when it was originally
introduced because of compatibility concerns, but now, 15+ years later, it's
probably safe enough to change this).

src/common/dlgcmn.cpp

@@ -78,7 +78,6 @@ wxFLAGS_MEMBER(wxTAB_TRAVERSAL)
 wxFLAGS_MEMBER(wxCLIP_CHILDREN)
 
 // dialog styles
-wxFLAGS_MEMBER(wxWS_EX_VALIDATE_RECURSIVELY)
 wxFLAGS_MEMBER(wxSTAY_ON_TOP)
 wxFLAGS_MEMBER(wxCAPTION)
 wxFLAGS_MEMBER(wxSYSTEM_MENU)