Remove a workaround for varargs not compiling on WASI.

This PR removes a workaround on WASI where we were avoiding a call to
`withVaList()` because it miscompiled there. That problem was fixed by
swiftlang/swift#84029 and cherry-picked to 6.2.

Author: grynspan

Sources/Testing/Events/TimeValue.swift

@@ -81,10 +81,6 @@ extension TimeValue: Codable {}
 
 extension TimeValue: CustomStringConvertible {
   var description: String {
-#if os(WASI)
-    // BUG: https://github.com/swiftlang/swift/issues/72398
-    return String(describing: Duration(self))
-#else
     let (secondsFromAttoseconds, attosecondsRemaining) = attoseconds.quotientAndRemainder(dividingBy: 1_000_000_000_000_000_000)
     let seconds = seconds + secondsFromAttoseconds
     var milliseconds = attosecondsRemaining / 1_000_000_000_000_000
@@ -98,7 +94,6 @@ extension TimeValue: CustomStringConvertible {
       }
       return String(cString: buffer.baseAddress!)
     }
-#endif
   }
 }