Remove @objc SVGImage

[swhitty]

Converts class SVG to struct SVG removing @objc(SVGImage) as it does not expose any useful functionality.

[codecov]

Codecov Report

Attention: Patch coverage is 78.57143% with 9 lines in your changes missing coverage. Please review.

Project coverage is 84.70%. Comparing base (b1d4a2d) to head (79a5130).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
SwiftDraw/SVG.swift	65.38%	9 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #69   +/-   ##
=======================================
  Coverage   84.70%   84.70%           
=======================================
  Files          79       81    +2     
  Lines        7242     7242           
=======================================
  Hits         6134     6134           
  Misses       1108     1108           

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