remove stale netty dependencies

[isegall-da]

Fixes https://github.com/DACH-NY/cn-test-failures/issues/6937

AFAICT:
Canton moved to grpc-netty-shaded here

We adopted the addition of grpc-netty-shaded, but did not remove the other netty stuff that they did, and are now getting a blackduck alert on it.

Hopefully if this passes CI that means we can safely just remove it?

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[moritzkiefer-da]

@isegall-da The CI failures seem genuine, I'd prbably suggest to wait for https://github.com/DACH-NY/canton/pull/30331 to be sorted out first before we try bumping bouncy castle on our side.