refactor: remove deeppavlov.configs.skills

Created by: IgnatovFedor

Removed configuration files:

• deeppavlov/configs/skills/aiml_skill.json
• deeppavlov/configs/skills/dsl_skill.json
• deeppavlov/configs/skills/rasa_skill.json

Removed components:

• aiml_skill
• rasa_skill
• DSLSkill