Remove apparent contradiction in vector.h header

3205a92ad8 was a major commit which removed `PoolVector`, and replaced
most references to `PoolVector` with `Vector` instead. In most cases,
this was appropriate, given that `PoolVector` was being replaced with
`Vector`, as an effective generalist in 64-bit address space layouts.

However, vector.h itself was left with an artifact advising the reader
to use `Vector` instead of `Vector` for large arrays. While this led
to a fascinating deep dive, and hopefully improved some of the
documentation along the way, it's probably best to clean this up for
the next person.

core/templates/vector.h

@@ -33,7 +33,10 @@
 
 /**
  * @class Vector
- * Vector container. Regular Vector Container. Use with care and for smaller arrays when possible. Use Vector for large arrays.
+ * Vector container. Simple copy-on-write container.
+ *
+ * LocalVector is an alternative available for internal use when COW is not
+ * required.
  */
 
 #include "core/error/error_macros.h"