fix: reobfuscated jar should not contain mapping information

[PierreSchwang]

Overview

Follow-up PR. Drops the paperweight-mappings-namespace manifest entry for the reobfuscated JARs, which prevented the FAWE-Spigot JARs to be remapped by Paper on startup (therefor fail)

Submitter Checklist

• Make sure you are opening from a topic branch (/feature/fix/docs/ branch (right side)) and not your main branch.
• Ensure that the pull request title represents the desired changelog entry.
• New public fields and methods are annotated with @since TODO.
• I read and followed the contribution guidelines.

[SirYwell]

Looks reasonable