Use on_ubuntucore function from checkbox-support snapd_utils helpers (bugfix)

[pieqq]

Description

There should be only one canonical way to check if a script is being run on Ubuntu Core or not. Use the on_ubuntucore function provided by checkbox-support snap_utils in the removable storage test script.

Resolved issues

Fix CER-2892

Documentation

Tests

• The function provided in checkbox-support works as expected on Ubuntu Core (it was tested on an actual device running UC20 in the lab) and on classic

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 50.46%. Comparing base (983792c) to head (fafe671).
⚠️ Report is 144 commits behind head on main.

Files with missing lines	Patch %	Lines
providers/base/bin/removable_storage_test.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1853   +/-   ##
=======================================
  Coverage   50.45%   50.46%           
=======================================
  Files         382      382           
  Lines       41026    41018    -8     
  Branches     6890     6886    -4     
=======================================
  Hits        20698    20698           
+ Misses      19584    19577    -7     
+ Partials      744      743    -1     

Flag	Coverage Δ
provider-base	26.69% <0.00%> (+0.01%)	⬆️

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[fernando79513]

LGTM+1!