Remove many "versionchanged" items that didn't use the official markup,
but just some text embedded in the docs.

Also remove paragraph about implicit relative imports from tutorial.
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
index b7dd32f..7052c7b 100644
--- a/Doc/library/decimal.rst
+++ b/Doc/library/decimal.rst
@@ -766,9 +766,8 @@
 
    Set the current context for the active thread to *c*.
 
-Beginning with Python 2.5, you can also use the :keyword:`with` statement and
-the :func:`localcontext` function to temporarily change the active context.
-
+You can also use the :keyword:`with` statement and the :func:`localcontext`
+function to temporarily change the active context.
 
 .. function:: localcontext([c])