Swift: Update PoundDiagnosticDecl test

These elements are no longer present in the Swift 6.2 AST.

Author: jketema

swift/ql/test/extractor-tests/generated/decl/PoundDiagnosticDecl/PoundDiagnosticDecl.expected

@@ -1,4 +1,2 @@
 instances
-| diagnostics.swift:2:1:2:25 | #warning(...) | getModule: | file://:0:0:0:0 | diagnostics | getKind: | 2 | getMessage: | diagnostics.swift:2:10:2:10 | I'm a warning |
-| diagnostics.swift:3:1:3:26 | #error(...) | getModule: | file://:0:0:0:0 | diagnostics | getKind: | 1 | getMessage: | diagnostics.swift:3:8:3:8 | And I'm an error |
 getMember