[Twig] Hide internal parameter in tail completion of extensions

[Haehnchen]

first method parameter in most twig extension are twig internals, remove them from completion visibility

[stof]

@Haehnchen a Twig function can actually have 2 internal parameters (added in the first places when needed):

• the environment based on needs_environment in the function options
• the current context (which is an array) based on needs_context.

[Haehnchen]

thx doc: http://twig.sensiolabs.org/doc/advanced.html#context-aware-filters