lib/remote: Export ostree_remote_get_type symbol

Without this, you can't really use OstreeRemote as a GObject, which is a
requirement for bindings.

This was found when attempting to include OstreeRemote in the GIR, and
g-ir-scanner wasn't able to link it's temporary object due to an
"undefined reference to `ostree_remote_get_type'" error.

Closes: #1337
Approved by: pwithnall

src/libostree/libostree-experimental.sym

@@ -89,3 +89,8 @@ global:
   ostree_repo_finder_override_get_type;
   ostree_repo_finder_override_new;
 } LIBOSTREE_2017.12_EXPERIMENTAL;
+
+LIBOSTREE_2017.14_EXPERIMENTAL {
+global:
+  ostree_remote_get_type;
+} LIBOSTREE_2017.13_EXPERIMENTAL;