NLua: remove this[string field] overloads on LuaTable and LuaUserData

- closes #4387

Those overloads try to imitate lua's "a.b" parsing by navigating tables recursively, e.g. `table["a.b"]` == `table.a.b`. This is not what's intended by 100% of the use cases of these overloads, so I've removed them.

ExternalProjects/NLua/src/Lua.cs

@@ -890,6 +890,7 @@ namespace NLua
 			return obj;
 		}
 
+#if false
 		/// <summary>
 		/// Gets a field of the table or userdata corresponding to the provided reference
 		/// </summary>
@@ -901,9 +902,10 @@ namespace NLua
 			State.SetTop(oldTop);
 			return returnValue;
 		}
+#endif
 
 		/// <summary>
-		/// Gets a numeric field of the table or userdata corresponding to the provided reference
+		/// Gets a field of the table or userdata corresponding to the provided reference
 		/// </summary>
 		internal object GetObject(int reference, object field)
 		{
@@ -916,6 +918,7 @@ namespace NLua
 			return returnValue;
 		}
 
+#if false
 		/// <summary>
 		/// Sets a field of the table or userdata corresponding to the provided reference
 		/// to the provided value
@@ -927,9 +930,10 @@ namespace NLua
 			SetObject(FullPathToArray(field), val);
 			State.SetTop(oldTop);
 		}
+#endif
 
 		/// <summary>
-		/// Sets a numeric field of the table or userdata corresponding to the provided reference
+		/// Sets a field of the table or userdata corresponding to the provided reference
 		/// to the provided value
 		/// </summary>
 		internal void SetObject(int reference, object field, object val)

ExternalProjects/NLua/src/LuaTable.cs

@@ -25,6 +25,7 @@ namespace NLua
 		{
 		}
 
+#if false
 		/// <summary>
 		/// Indexer for string fields of the table
 		/// </summary>
@@ -41,10 +42,8 @@ namespace NLua
 				lua.SetObject(_Reference, field, value);
 			}
 		}
+#endif
 
-		/// <summary>
-		/// Indexer for numeric fields of the table
-		/// </summary>
 		public object this[object field]
 		{
 			get => !TryGet(out var lua) ? null : lua.GetObject(_Reference, field);

ExternalProjects/NLua/src/LuaUserData.cs

@@ -10,6 +10,7 @@ namespace NLua
 		{
 		}
 
+#if false
 		/// <summary>
 		/// Indexer for string fields of the userdata
 		/// </summary>
@@ -26,10 +27,8 @@ namespace NLua
 				lua.SetObject(_Reference, field, value);
 			}
 		}
+#endif
 
-		/// <summary>
-		/// Indexer for numeric fields of the userdata
-		/// </summary>
 		public object this[object field]
 		{
 			get => !TryGet(out var lua) ? null : lua.GetObject(_Reference, field);