[Kotlin][Multiplatform] Fix Enum Generation

Created by: tkirshboim

PR Description

Fixes #10902 (closed)

• Fix broken generation of enum classes by removing unnecessary template code that broke the compilation of the generated code.

Testing

Reproducing the issue

To validate that this PR fixes the issue you should first reproduce the issue. This can be done on the master branch by generating the kotlin-multiplatform template code with the petstore-with-fake-endpoints-models-for-testing.yaml API spec, and then trying to compile the generated code:

./bin/generate-samples.sh bin/configs/kotlin-multiplatform.yaml -- -i modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
./mvnw integration-test -f samples/client/petstore/kotlin-multiplatform/pom.xml

The test fails due to several compilation errors. The errors that are relevant for the purpose of this PR, as reported in #10902 (closed) , can be observed in OuterEnum.kt and EnumClass.kt:

[redacted]
e: ./openapi-generator/samples/client/petstore/kotlin-multiplatform/src/commonMain/kotlin/org/openapitools/client/models/EnumClass.kt: (31, 32): Unresolved reference: Serializer
[redacted]
e: ./openapi-generator/samples/client/petstore/kotlin-multiplatform/src/commonMain/kotlin/org/openapitools/client/models/OuterEnum.kt: (31, 32): Unresolved reference: Serializer

To validate that this PR fixes the issue, checkout this PR's code and re-run the two commands from above. The compile errors in OuterEnum.kt and EnumClass.kt are no longer present.

CCs

Kotlin technical committee: @jimschubert @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m

Reporter of #10902 (closed) : @Qbit982

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  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*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.