bpo-38872: Document exec symbol for codeop.compile_command (GH-20047)

* Document exec symbol for codeop.compile_command

* Remove extra statements

Co-authored-by: nanjekyejoannah <joannah.nanjekye@ibm.com>
diff --git a/Doc/library/code.rst b/Doc/library/code.rst
index 6708079..538e5af 100644
--- a/Doc/library/code.rst
+++ b/Doc/library/code.rst
@@ -56,8 +56,8 @@
 
    *source* is the source string; *filename* is the optional filename from which
    source was read, defaulting to ``'<input>'``; and *symbol* is the optional
-   grammar start symbol, which should be either ``'single'`` (the default) or
-   ``'eval'``.
+   grammar start symbol, which should be ``'single'`` (the default), ``'eval'``
+   or ``'exec'``.
 
    Returns a code object (the same as ``compile(source, filename, symbol)``) if the
    command is complete and valid; ``None`` if the command is incomplete; raises