Make tp_str_empty() a static inline function directly
Make tp_str_empty() a static inline function directly

The
tp_str_empty()-is-a-macro-which-is-implemented-as-a-static-inline-function
thing was a workaround for gtk-doc not supporting static inline
functions.

As of 1.16, it does.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib