regex: tweak DFA settings

This increases the limits a bit for when the regex engine will build and
use a fully compiled DFA. They can faster in some circumstances. For
example, '(?-u)^\w{30,}$' gets a nice speed boost from state
acceleration.

We are also able to remove `regex` proper as a dependency. Wow.

Cargo.lock

@@ -200,7 +200,6 @@ dependencies = [
  "bstr",
  "grep-matcher",
  "log",
- "regex",
  "regex-automata 0.3.0",
  "regex-syntax",
 ]