After we upgrade the projects under Runtime.sln to .NET 4.5, we need to reivew and cleanup the source code to make sure we're taking full use of .NET 4.5.
Consider the followings:
* Remove ParameterInfoExtensions.GetCustomAttributes<TAttribute> and use .NET 4.5's CustomAttributeExtensions.GetCustomAttributes<T>
* Remove the package dependency on Microsoft.Web.Infrastructure. Should be able to use everything from System.Web
* Remove MachineKey40CryptoSystem, no longer needed for 4.5
* Review the use of obsolete APIs MachineKey.Encode/Decode
* Remove the System.Web.Helpers.UnvalidatedRequestValues class, this can be replaced with System.Web.UnvalidatedRequestValues
* Consider removing System.Web.Helpers.Validation extensions, should just use Request.Unvalidated that's available in 4.5