docs: Simplify the text for g_array_free
docs: Simplify the text for g_array_free

The text about deallocation of GArrays with elements containing
dynamically-allocated memory was confusing. It initially mentioned
clear_func, but later said elements with dynamically allocated memory
"should be freed separately".

Clarify this by using the same structure as g_ptr_array_free —
highlight the need to set a clear_func by consolidating the text about
it in a separate paragraph.

https://gitlab.gnome.org/GNOME/glib/merge_requests/348

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib