Move in common a property duplicated since connection manager own move.

Author: fredericDelaporte

src/NHibernate/Impl/AbstractSessionImpl.cs

@@ -32,6 +32,9 @@ public abstract partial class AbstractSessionImpl : ISessionImplementor
 
 		private bool closed;
 
+		/// <summary>Get the current NHibernate transaction.</summary>
+		public ITransaction Transaction => ConnectionManager.Transaction;
+
 		protected bool TransactionCoordinatorShared { get; }
 
 		public ITransactionContext TransactionContext

src/NHibernate/Impl/SessionImpl.cs

@@ -1286,11 +1286,6 @@ public void Refresh(object obj, LockMode lockMode)
 			}
 		}
 
-		public ITransaction Transaction
-		{
-			get { return ConnectionManager.Transaction; }
-		}
-
 		/// <summary>
 		///
 		/// </summary>

src/NHibernate/Impl/StatelessSessionImpl.cs

@@ -376,12 +376,6 @@ public override bool TransactionInProgress
 
 		#region IStatelessSession Members
 
-		/// <summary> Get the current Hibernate transaction.</summary>
-		public ITransaction Transaction
-		{
-			get { return ConnectionManager.Transaction; }
-		}
-
 		public override CacheMode CacheMode
 		{
 			get { return CacheMode.Ignore; }