gtk headers : Fix typedef redeclaration of GMainContext and GdkPixbuf

The following typedef redeclaration warnings were seen on Solaris in 11u but on examination it seems it is an issue in all releases including mainline, but only the Solaris compiler warns.
 
Two typedef declarations are causing this issue - GMainContext, GdkPixbuf

The problem is that they are defined in gtk_interface.h but then redefined in gtk2_interface.h and gtk3_interface.h
The fix is to remove the redeclarations in gtk2_interface.h and gtk3_interface.h

[2024-07-14T16:49:41,763Z] === Output from failing command(s) repeated here ===
[2024-07-14T16:49:41,767Z] * For target support_native_java.desktop_libawt_xawt_gtk2_interface.o:
[2024-07-14T16:49:41,772Z] "open/src/java.desktop/unix/native/libawt_xawt/awt/gtk2_interface.h", line 53: error: typedef redeclared: GMainContext (E_TYPEDEF_REDECLARED)
[2024-07-14T16:49:41,772Z] cc: acomp failed for ./open/src/java.desktop/unix/native/libawt_xawt/awt/gtk2_interface.c
[2024-07-14T16:49:41,782Z] * For target support_native_java.desktop_libawt_xawt_gtk3_interface.o:
[2024-07-14T16:49:41,787Z] "open/src/java.desktop/unix/native/libawt_xawt/awt/gtk3_interface.h", line 179: error: typedef redeclared: GMainContext (E_TYPEDEF_REDECLARED)