eslint automatic fixes

[lindapaiste]

PR #1379 introduces new eslint rules, which I suppressed in that PR. Here I am actually remedying a bunch of them in the code.

• Ran npx eslint src --fix to automatically fix all violations for rules:
  • arrow-body-style
  • import/no-useless-path-segments
  • no-else-return
  • prefer-regex-literals
  • prefer-object-spread
  • lines-between-class-members
• Deleted a handful of useless = null default parameters which violated default-param-last
• Rewrote one regex which violated prefer-regex-literals

Fixed in other PRs:

• 3/4 violations of no-constructor-return are fixed by Refactor: breakup ImageClassifier #1362
• 1/2 violations of prefer-regex-literals is deleted in Better handling of model URL formation #1376

Prior to fixing, these are the counts of violations in /src (including test files):

All violations of no-unused-vars are in test files (this rule is not new).