docs: Remove the term "wrapper"

This committed the sin of introducing a concept by giving it two
names:

> An alias, or wrapper, around ``ls`` might look like this

The term "wrapper" doesn't pull its weight here. It's simpler to just
call them aliases throughout. We do use "a simple wrapping function"
in another place, but that's to define "alias", not as a separate name.

doc_src/cmds/alias.rst

@@ -59,4 +59,4 @@ See more
 
 1. The :doc:`function <function>` command this builds on.
 2. :ref:`Functions <syntax-function>`.
-3. :ref:`Function wrappers <syntax-function-wrappers>`.
+3. :ref:`Defining aliases <syntax-aliases>`.