girepository: Remove _ prefix from private functions

Now that libgirepository uses `GI_AVAILABLE_IN_*` macros, that’s what
controls symbol visibility. The `_` prefixes are redundant, and out of
keeping with the rest of GLib.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3155

girepository/givfuncinfo.c

@@ -45,10 +45,10 @@
  */
 
 GIVFuncInfo *
-_gi_base_info_find_vfunc (GIRealInfo  *rinfo,
-                          guint32      offset,
-                          gint         n_vfuncs,
-                          const gchar *name)
+gi_base_info_find_vfunc (GIRealInfo  *rinfo,
+                         guint32      offset,
+                         gint         n_vfuncs,
+                         const gchar *name)
 {
   /* FIXME hash */
   Header *header = (Header *)rinfo->typelib->data;