(#20520) Update rgen to 0.6.2, remove Array monkey patches

Monkey patches to Array were used to make Array#to_hash fail, which otherwise
broke Hash[[[]].  The later version of rgen removes the need for these, which
prevents bad interactions with other libraries and applications.
Merge pull request #1631 from domcleal/tickets/stable/20520-rgen-062

(#20520) Update rgen to 0.6.2, remove Array monkey patches