Remove requirement for equal X and Y resolution in conv2tif

[mcgarth]

This PR removes a long-held rule in conv2tif that the input rasters must have equal X and Y pixel resolutions.

This issue was identified by an external user who has unequal X/Y resolution images - see #305

In this PR I have removed:

• one check in the function shared.write_fullres_geotiff, used only in conv2tif step
• the check function associated with the above
• two tests associated with the check function

[codecov-io]

Codecov Report

Merging #306 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #306      +/-   ##
==========================================
- Coverage   83.22%   83.20%   -0.03%     
==========================================
  Files          26       26              
  Lines        3470     3465       -5     
  Branches      544      542       -2     
==========================================
- Hits         2888     2883       -5     
  Misses        486      486              
  Partials       96       96              

Impacted Files	Coverage Δ
pyrate/core/shared.py	93.08% <ø> (-0.07%)	⬇️

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