[MRG] remove unnecessary downsampling warnings

[ctb]

Addresses the (unnecessary) warnings output in #1970 (comment); removes this output,

downsampling query from 1 to 1

when the numbers are equal.

[codecov]

Codecov Report

Merging #1971 (ac2332c) into latest (2d1fc69) will increase coverage by 7.90%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           latest    #1971      +/-   ##
==========================================
+ Coverage   83.54%   91.44%   +7.90%     
==========================================
  Files         127       96      -31     
  Lines       14235     9955    -4280     
  Branches     1946     1946              
==========================================
- Hits        11892     9103    -2789     
+ Misses       2070      579    -1491     
  Partials      273      273              

Flag	Coverage Δ
python	91.44% <100.00%> (ø)
rust	?

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Impacted Files	Coverage Δ
src/sourmash/commands.py	88.37% <100.00%> (ø)
src/core/src/lib.rs
src/core/src/sketch/minhash.rs
src/core/src/index/bigsi.rs
src/core/src/errors.rs
src/core/src/ffi/cmd/compute.rs
src/core/src/ffi/nodegraph.rs
src/core/src/index/search.rs
src/core/src/cmd.rs
src/core/src/storage.rs
... and 22 more

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[ctb]

ready for review & merge @sourmash-bio/devs - this is an easy one ;)