Remove note from docker version 1.3 on Env variables
Fixes
@@ -114,12 +114,6 @@ images.
### Environment replacement
-> **Note**: prior to 1.3, `Dockerfile` environment variables were handled
-> similarly, in that they would be replaced as described below. However, there
-> was no formal definition on as to which instructions handled environment
-> replacement at the time. After 1.3 this behavior will be preserved and
-> canonical.
-
Environment variables (declared with [the `ENV` statement](#env)) can also be
used in certain instructions as variables to be interpreted by the
`Dockerfile`. Escapes are also handled for including variable-like syntax
