Restore configure tests disabled by GTK1 support removal

The changes of fb4f0b590c (Remove wxGTK1 port and GPE support,
2022-10-16) accidentally disabled several checks that were supposed to
be done when using wxGTK, notably for GTK print library.

This was due to WXGTK2 not being defined any longer and is fixed now by
replacing the tests for it with tests for wxUSE_GTK (as WXGTK2 used to
mean "any GTK version other than 1", and not "GTK version 2").

Closes #22994.

configure.in

@@ -4778,11 +4778,7 @@ if test "$wxUSE_DEBUG_FLAG" = "no" ; then
     WXCONFIG_CPPFLAGS="$WXCONFIG_CPPFLAGS -DwxDEBUG_LEVEL=0"
 
     if test "$wxUSE_GTK" = 1 ; then
-        if test "$WXGTK2" = 1 ; then
-            CPPFLAGS="$CPPFLAGS -DG_DISABLE_CAST_CHECKS"
-        else
-            CPPFLAGS="-DGTK_NO_CHECK_CASTS $CPPFLAGS"
-        fi
+        CPPFLAGS="$CPPFLAGS -DG_DISABLE_CAST_CHECKS"
     fi
 fi
 
@@ -5215,7 +5211,7 @@ if test "$wxUSE_SOUND" = "yes"; then
   SAMPLES_SUBDIRS="$SAMPLES_SUBDIRS sound"
 fi
 
-if test "$WXGTK2" = 1; then
+if test "$wxUSE_GTK" = 1; then
     if test "$wxUSE_PRINTING_ARCHITECTURE" = "yes" ; then
 
         if test "$wxUSE_GTKPRINT" = "yes" ; then
@@ -7763,12 +7759,8 @@ AC_SUBST(USE_DPI_AWARE_MANIFEST)
 case "$TOOLKIT" in
     GTK)
         TOOLKIT_DESC="GTK+"
-        if test "$WXGTK2" = 1; then
-            if test "$WXGTK3" = 1; then
-                TOOLKIT_DESC="$TOOLKIT_DESC ${TOOLKIT_VERSION}"
-            else
-                TOOLKIT_DESC="$TOOLKIT_DESC 2"
-            fi
+        if test "$wxUSE_GTK" = 1; then
+            TOOLKIT_DESC="$TOOLKIT_DESC ${TOOLKIT_VERSION}"
             if test "$wxUSE_GTKPRINT" = "yes" ; then
                 TOOLKIT_EXTRA="$TOOLKIT_EXTRA GTK+ printing";
             fi