Remove unsound quantifier reduction rules.

[jirkamarsik]

Some of the quantifier reduction rules in oniguruma are invalid, leading to new regular expressions with different semantics. This PR removes two such reduction rules.

Here they are illustrated. If we introduce a capture group in between the two quantifiers, we prevent the quantifier reduction from triggering, leading to a different result.

irb(main):001:0> /(?:a+?)*/.match("aa")
=> #<MatchData "a">
irb(main):002:0> /(a+?)*/.match("aa")
=> #<MatchData "aa" 1:"a">
irb(main):003:0> /(?:a+?)+/.match("aa")
=> #<MatchData "a">
irb(main):004:0> /(a+?)+/.match("aa")
=> #<MatchData "aa" 1:"a">

I have reported the issue to MRI Ruby. This PR is a port of their PR.

https://bugs.ruby-lang.org/issues/17341
ruby/ruby#3808

[headius]

LGTM. Were tests added for this somewhere?

[jirkamarsik]

MRI Ruby added a test in test/ruby/test_regexp.rb.
https://github.com/ruby/ruby/pull/3808/files#diff-f12a6f58c06015b85739069cde86a0921a8f12fb9c66e05e6643f6dbcebb1a29