Remove warning silence on Journey::Parser require

I assume this was originally [added][1] because `Parser` was generated
by `racc`, and parser generators have historically emitted many Ruby
warnings.

However, now the parser is no longer generated by `racc` so the warning
silencing is unnecessary (and could potentially cover up legitimate and
fixable warnings in the hand written parser).

[1]: rails/journey@53951dc

Author: skipkayhil

actionpack/lib/action_dispatch/journey/router.rb

@@ -5,12 +5,7 @@
 require "action_dispatch/journey/router/utils"
 require "action_dispatch/journey/routes"
 require "action_dispatch/journey/formatter"
-
-before = $-w
-$-w = false
 require "action_dispatch/journey/parser"
-$-w = before
-
 require "action_dispatch/journey/route"
 require "action_dispatch/journey/path/pattern"