Remove image-proc feature and functions to generate a thumbnail

[zecakeh]

Since no one seems to use it, according to our discussion in the Dev room.

The second commit, on top of the first, allows to remove a bunch of dependencies in Cargo.lock.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.70%. Comparing base (ee4ef2e) to head (8504ff7).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4132      +/-   ##
==========================================
- Coverage   84.72%   84.70%   -0.02%     
==========================================
  Files         269      269              
  Lines       28837    28770      -67     
==========================================
- Hits        24432    24371      -61     
+ Misses       4405     4399       -6     

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[jmartinesp]

Thanks!