Stop using env.dynamic in parsers. (whitequark)

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 9115]
+ Removed RubyLexer#tern. Introduced and disused during 3.0 alpha. (whitequark)
+ Removed Env#dynamic, #dynamic?, #use, #used?

[git-p4: depot-paths = "//src/ruby_parser/dev/": change = 9116]