Remove erroneous ENTRYPOINT note

The Dockerfile parser does not subsitute ENV variables in any form of
the ENTRYPOINT command.  Any substitution, if done, is done by the shell
when the command is executed.

Signed-off-by: David Dooling <dooling@gmail.com>

docs/reference/builder.md

@@ -1075,8 +1075,6 @@ sys	0m 0.03s
 > `ENTRYPOINT [ "echo", "$HOME" ]` will not do variable substitution on `$HOME`.
 > If you want shell processing then either use the *shell* form or execute
 > a shell directly, for example: `ENTRYPOINT [ "sh", "-c", "echo $HOME" ]`.
-> Variables that are defined in the `Dockerfile`using `ENV`, will be substituted by
-> the `Dockerfile` parser.
 
 ### Shell form ENTRYPOINT example