Remove twig form themes config

[Hanmac]

Subject

I am targeting this branch, because its BC.

Closes #1699.

Changelog

### Removed
- Removed twig form themes from SonataPageExtension

[Hanmac]

hm i need to check what is wrong with the tests, normally PageBundle should have defined the values

[Hanmac]

as for more tests, I'm going to add more tests soon to form-extensions to check that twig theme definitions

[VincentLanglet]

as for more tests, I'm going to add more tests soon to form-extensions to check that twig theme definitions

You mean in this Pr or another ?

[Hanmac]

as for more tests, I'm going to add more tests soon to form-extensions to check that twig theme definitions

You mean in this Pr or another ?

different project

i noticed that there are some Tests missing in the form-extensions project
(like using MockObject for Twig Extension to see if the config gets extended)
and i would add the test case later there

as for the test in this project, i only found this sonata-project/SonataUserBundle#924 and sonata-project/SonataUserBundle#925
when searching twig.form.resources but i don't know how to fix the test for the page bundle so i removed it

similar tests like in sonata-project/SonataUserBundle#925 will be later added into form-extensions

[VincentLanglet]

Thanks