(#22962) Remove alternative lambda syntaxes from tests

Conflicts:
	spec/unit/parser/methods/collect_spec.rb
	spec/unit/parser/methods/reject_spec.rb
	spec/unit/parser/methods/select_spec.rb
(#22969) Remove alternative lambda syntax

This removes the two alternative lambda syntax forms from the grammar
and changes (and removes) tests that were testing (or using) the
removed forms.

The two removed forms are:
* {|$x| }
* |$x| => { }
Merge pull request #2011 from hlindberg/feature/22962-remove-alt-lambda

(#22962) remove alternative lambda syntax