other: hide battery tab selector if there is only one battery

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Issue

If applicable, what issue does this address?

Closes: #1235

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 ⚠️

Comparison is base (3f53818) 31.86% compared to head (7fef0b5) 31.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1236      +/-   ##
==========================================
- Coverage   31.86%   31.86%   -0.01%     
==========================================
  Files          97       97              
  Lines       16573    16575       +2     
==========================================
  Hits         5281     5281              
- Misses      11292    11294       +2     

Flag	Coverage Δ
macos-12	33.44% <0.00%> (-0.01%)	⬇️
ubuntu-latest	33.44% <0.00%> (-0.01%)	⬇️
windows-2019	33.70% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/app.rs	1.48% <0.00%> (ø)
src/canvas/widgets/battery_display.rs	0.00% <0.00%> (ø)
src/data_conversion.rs	14.60% <0.00%> (+0.05%)	⬆️

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