Use g_list_free_full instead of g_list_foreach followed by g_list_free.
This fixes a compiler warning.

The g_list_foreach function takes a "GFunc" callback, which takes two
arguments, but the free functions we pass only take one argument, so the
compiler warns about an incompatible cast. Using g_list_free_full fixes
this because it takes a "GDestroyNotify" callback, which takes one
argument.