Remove [dev] extra when building docker container for Porter

[derekpierre]

Type of PR:

• Bugfix
• Feature
• Documentation
• Other

Required reviews:

• 1
• 2
• 3

What this does:

High-level idea of the changes introduced in this PR.
List relevant API changes (if any), as well as related PRs and issues.

Issues fixed/closed:

• Fixes #...

Closes #33 .

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network.
E.g., if this PR addresses a nucypher/productdev issue, let reviewers know!

Removal of prometheus imports for non-dev versions already addressed in nucypher. Subsequent prometheus work is being done in an EPIC branch.

Notes for reviewers:

What should reviewers focus on?
Is there a particular commit/function/section of your PR that requires more attention from reviewers?