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/Lib/codeop.py b/Lib/codeop.py
index 082285f..835e68c 100644
--- a/Lib/codeop.py
+++ b/Lib/codeop.py
@@ -112,7 +112,8 @@
     source -- the source string; may contain \n characters
     filename -- optional filename from which source was read; default
                 "<input>"
-    symbol -- optional grammar start symbol; "single" (default) or "eval"
+    symbol -- optional grammar start symbol; "single" (default), "exec"
+              or "eval"
 
     Return value / exceptions raised: