C#: Update expected output following roslyn-3.0.0 update.

Author: calumgrant

csharp/ql/test/library-tests/compilations/Compilations.expected

@@ -1,5 +1,4 @@
 diagnostics
-| Program.cs:1:1:1:13 | CS8019: Unnecessary using directive. | CS8019 | 0 | Unnecessary using directive | Unnecessary using directive. |
 | Program.cs:7:13:7:13 | CS0219: The variable 'x' is assigned but its value is never used | CS0219 | 2 | Variable is assigned but its value is never used | The variable 'x' is assigned but its value is never used |
 | Program.cs:9:9:9:11 | CS0162: Unreachable code detected | CS0162 | 2 | Unreachable code detected | Unreachable code detected |
 | Program.cs:9:13:9:13 | CS0219: The variable 'y' is assigned but its value is never used | CS0219 | 2 | Variable is assigned but its value is never used | The variable 'y' is assigned but its value is never used |
@@ -23,7 +22,6 @@ compilationFiles
 compilationFolder
 | compilation | compilations |
 diagnosticElements
-| Program.cs:1:1:1:13 | CS8019: Unnecessary using directive. | Program.cs:1:1:1:13 | using ...; |
 | Program.cs:7:13:7:13 | CS0219: The variable 'x' is assigned but its value is never used | Program.cs:7:13:7:13 | access to local variable x |
 | Program.cs:7:13:7:13 | CS0219: The variable 'x' is assigned but its value is never used | Program.cs:7:13:7:13 | x |
 | Program.cs:9:13:9:13 | CS0219: The variable 'y' is assigned but its value is never used | Program.cs:9:13:9:13 | access to local variable y |