Remove operators from regex builder.

https://github.com/apple/swift-experimental-string-processing/blob/main/Documentation/Evolution/RegexBuilderDSL.md#operators-for-quantification-and-alternation

Author: rxwei

Sources/RegexBuilder/DSL.swift

@@ -165,10 +165,6 @@ public struct Repeat<Output>: _BuiltinRegexComponent {
   // Variadics.swift.
 }
 
-postfix operator .?
-postfix operator .*
-postfix operator .+
-
 // MARK: Alternation
 
 // TODO: Variadic generics