Remove two accidentally-exported symbols

Remove two accidentally-exported symbols

This reverts commit 85976cf91deae6ac7cf1639a187a424ff7296968 and
properly removes the offending symbols from gio.symbols.

These two private symbols were found to be exported during Colin's
recent work cleaning up function visibility (among other things).

They were never exposed in any header file and I am 100% certain that
they have never been used by anybody.  They were always private -- only
exposed on the library symbol list.

This change will cause ABI checking tools to complain that we have
removed functions, but the change is completely harmless for actual
applications.

https://bugzilla.gnome.org/show_bug.cgi?id=687441