sample: Drop support for translation

[ryonakano]

This is just a sample so no need to mark these strings translatable.

[tintou]

Why not keeping it like this?

[ryonakano]

Either is fine, but since we don't provide translations of this file in the switchboard itself, I thought calling _() here is useless.

[ryonakano]

After reconsideration I'll close the PR because those who want to build a new plug based on the sample plug would take the trouble to add _() to display_name and description. Even though calling _() by this plug itself is useless, but by keeping it as it is, people just need to edit strings inside _().