p2p: replace `x25519-dalek` with `curve25519-dalek-ng`

[tony-iqlusion]

The tendermint-p2p crate previously pulled in both an obsolete version of x25519-dalek/curve25519-dalek, but also curve25519-dalek-ng by way of ed25519-consensus.

This replaces x25519-dalek with curve25519-dalek-ng which is already a dependency of ed25519-consensus. This reduces the overall number of dependencies and ensures curve25519-dalek-ng is the main Curve25519 implementation used.

Note: I don't have an open issue for this but since it reduces the overall number of dependencies I thought it made sense.

• [ ] Referenced an issue explaining the need for the change
• [ ] Updated all relevant documentation in docs
• [ ] Updated all code comments where relevant
• [ ] Wrote tests
• [ ] Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1370 (e91b0b4) into main (bcc0b37) will not change coverage. The diff coverage is 87.5%.

:exclamation: Current head e91b0b4 differs from pull request most recent head 7da8183. Consider uploading reports for the commit 7da8183 to get more accurate results

@@          Coverage Diff          @@
##            main   #1370   +/-   ##
=====================================
  Coverage   61.2%   61.2%           
=====================================
  Files        274     274           
  Lines      26844   26844           
=====================================
  Hits       16433   16433           
  Misses     10411   10411           

Files	Coverage Δ
p2p/src/secret_connection.rs	85.5% <100.0%> (ø)
test/src/test/unit/p2p/secret_connection.rs	100.0% <100.0%> (ø)
p2p/src/secret_connection/protocol.rs	59.8% <50.0%> (ø)

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