[Java][rest-assured] Remove stray Jackson 2 files from rest-assured-jackson3 sample

[ondrej-simon]

The Build Java Client JDK17 (samples/client/petstore/java/rest-assured-jackson3) job of the "Samples Java Client JDK17" workflow has been failing on master since #25112 (e.g. this run), and therefore on every PR that triggers this workflow:

RFC3339JavaTimeModule.java:[19,45] package com.fasterxml.jackson.databind.module does not exist
RFC3339InstantDeserializer.java:[26,34] package com.fasterxml.jackson.core does not exist
...

#25112 accidentally committed RFC3339InstantDeserializer.java and RFC3339JavaTimeModule.java into the rest-assured-jackson3 sample. These files are not generated for this config (they are not listed in .openapi-generator/FILES and nothing references them) and they import Jackson 2 packages, which are not on the classpath of the Jackson 3 sample.

This PR removes the two stray files. No generator or template changes.

Verified:

• ./bin/generate-samples.sh bin/configs/java-rest-assured-jackson3.yaml does not recreate the files and produces no other changes.
• mvn clean package of the sample (same command as CI) succeeds on JDK 17.

PR checklist

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

cc @wing328 (author of #25112), Java technical committee: @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @martin-mfg @KannaKim

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Summary by cubic

Removes two stray Jackson 2 files from the rest-assured-jackson3 sample that were accidentally committed and broke compilation in the "Samples Java Client JDK17" workflow. The files are not part of the generated output for this config and imported Jackson 2 packages that aren't on the classpath. No generator or template changes.

^{Written for commit f5b0567. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}