svg-aam: remove mappings for SVG elements removed between SVG2 2016 CR and SVG2 2018 CR

[dd8]

This issue tracks the changes required to align SVG AAM with the current SVG Candidate Rec
https://www.w3.org/TR/2018/CR-SVG2-20181004/changes.html

• Remove hatch and hatchpath element mappings
• Remove mesh gradients (including mesh, meshrow, and meshpath) element mappings
• Remove the solidcolor element mapping

https://www.w3.org/TR/2018/CR-SVG2-20181004/changes.html#pservers

• Remove the cursor element mapping

https://www.w3.org/TR/2018/CR-SVG2-20181004/changes.html#interact

See #42