Fix docs to account for license header.

lib/spack/docs/features.rst

@@ -102,6 +102,7 @@ It typically doesn't take much python coding to get from there to a
 working package file:
 
 .. literalinclude:: ../spack/packages/libelf.py
+   :lines: 25-
 
 Spack also provides wrapper functions around common commands like
 ``configure``, ``make``, and ``cmake`` to make writing packages

lib/spack/docs/packaging_guide.rst

@@ -42,6 +42,7 @@ It's probably easiest to learn about packages by looking at an
 example.  Let's take a look at ``libelf.py``:
 
 .. literalinclude:: ../spack/packages/libelf.py
+   :lines: 25-
    :linenos:
 
 Directory Structure