[MRG] remove 10x support

[luizirber]

See #1158 for discussion.

TODO for 4.0 release

• point to alternatives (kmermaid, as discussed in [MRG] Explore addition of a sketch command. #1159 (comment))

Checklist

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[codecov]

Codecov Report

Merging #1229 into latest will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           latest    #1229      +/-   ##
==========================================
- Coverage   83.34%   83.29%   -0.06%     
==========================================
  Files         103      103              
  Lines        9620     9588      -32     
==========================================
- Hits         8018     7986      -32     
  Misses       1602     1602              

Flag	Coverage Δ
rusttests	67.54% <ø> (ø)

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Impacted Files	Coverage Δ
sourmash/cli/compute.py	100.00% <ø> (ø)
sourmash/command_compute.py	97.51% <ø> (-0.20%)	⬇️
sourmash/command_sketch.py	89.93% <ø> (-0.19%)	⬇️
src/core/src/cmd.rs	86.88% <ø> (ø)

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[luizirber]

Ready for review and merge @ctb @olgabot