refactor(theme): delete duplicated and unused theme file

[pelord]

Please check if the PR fulfills these requirements

• [ ] The commit message follows our guidelines:https://github.com/infra-geo-ouverte/igo2/blob/master/.github/CONTRIBUTING.md#git-commit-guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

What is the current behavior? (You can also link to an open issue here) This file is not used and a duplicate from the igo2-lib.

What is the new behavior? Delete it. NOW.

Does this PR introduce a breaking change? (check one with "x")

[ ] Yes
[x] No

If this PR contains a breaking change, please describe the impact and migration path for existing applications:

Other information: