[clang][test][NFC] Also test for serialization in AST dump tests, part 1/n.

The outputs between the direct ast-dump test and the ast-dump test after
deserialization should match modulo a few differences.

For hand-written tests, strip the "<undeserialized declarations>"s and
the "imported"s with sed.

For tests generated with "make-ast-dump-check.sh", regenerate the
output.

Part 1/n.