Revert "Correctly parse comments in doctype declarations"

[greg-at-moderne]

Reverts #5581
as it's causing downstream problems, e.g.

/home/runner/work/rewrite-java-security/rewrite-java-security/src/main/java/org/openrewrite/java/security/xml/ExternalDTDAccumulator.java:32: error: incompatible types: Content cannot be converted to Element
                    for (Xml.Element element : docTypeDecl.getExternalSubsets().getElements()) {

Also this comment:
#5581 (comment)
needs to be addressed.

[MBoegers]

We should defnetly have a second look if we could find a way to do both ;)

[greg-at-moderne]

FYI @jhl221123

[jhl221123]

@greg-at-moderne, Thanks for the heads-up and for handling the revert so quickly. My apologies that my change caused this downstream issue; Please let me know if there's anything I can do to assist with the new approach.