[GTK] Exports leveldb symbols
https://bugs.webkit.org/show_bug.cgi?id=112526

Reviewed by Carlos Garcia Campos.

* Source/autotools/symbols.filter: make leveldb symbols local.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146059 268f45cc-cd09-0410-ab3c-d52691b4dbfc