gdb/dwarf: remove cooked_index::vec_type

I find this typedef to be confusing.  The name is a bit too generic, so
it's not clear what it represents.  When using the typedef for a
cooked_index_shard unique pointer, I think that spelling out the vector
type is not overly long.

Change-Id: I99fdab5cd925c37c3835b466ce40ec9c1ec7209d
Approved-By: Tom Tromey <tom@tromey.com>

gdb/dwarf2/cooked-index.c

@@ -647,7 +647,8 @@ cooked_index::wait (cooked_state desired_state, bool allow_quit)
 }
 
 void
-cooked_index::set_contents (vec_type &&vec, deferred_warnings *warn,
+cooked_index::set_contents (std::vector<cooked_index_shard_up> &&vec,
+			    deferred_warnings *warn,
 			    const parent_map_map *parent_maps)
 {
   gdb_assert (m_vector.empty ());