Unnecessary nvtx dependency

[yousefmoazzam]

This is likely leftover from when there used to be nvtx usage directly in httomo:

httomo/conda/environment.yml

Line 16 in f619ed1

- nvtx

However, it looks like nvtx is not used anywhere in the httomo codebase anymore (all usages must have gone into the methods repos, which would make sense), so this dependency in httomo can probably be removed.