There doesn't seem to be much need for these and they look a little different from the rest of Geany (or a lot different when Windows uses the dark theme and Geany the light one). Before removing the native win32 file open dialogs, win32_message_dialog() was called from the native file dialog implementations so its presence was necessary but I think normal GTK dialogs will serve their purpose well.
This is just a suggestion, anyone please feel free to disagree :-)
Also, completely untested - I'll only be able to test it on Windows at the end of the week. You can view, comment on, or merge this pull request online at:
https://github.com/geany/geany/pull/3903
-- Commit Summary --
* Drop win32_message_dialog()s
-- File Changes --
M src/dialogs.c (35) M src/win32.c (61) M src/win32.h (2)
-- Patch Links --
https://github.com/geany/geany/pull/3903.patch https://github.com/geany/geany/pull/3903.diff