drop non-existent feature from comment

Dependencies

• [2] JCSLDGAH beginnings of support for multiple shapes
• [3] QW5KQQTD fix a comment
• [4] VVXVV2D2 change data model; text can now have metadata
• [*] OTIBCAUJ love2d scaffold

Change contents

• edit in main.lua at line 36
  [2.500]→[2.500:547](∅→∅)
  − -- p1, p2, arrow-mode for mode 'arrow-line'