Remove enable_yui_compressor

Remove `enable_yui_compressor` as a option since this can be handled by using `assetic` configuration like:
```
assetic:
    # java: "/usr/bin/java"
    filters:
        yui_css:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"
            apply_to: "\.css$"
        yui_js:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"
            apply_to: "\.js$"
```
This should be a better way and reduce some template and configuration code.