Remove extra comparation of release_state in ProcessDefinitionMapper

[Mahongsheng]

Purpose of the pull request

This pull request fix /v2/workflows/query api.

In this api, there is a method called:

IPage<ProcessDefinition> filterProcessDefinition(IPage<ProcessDefinition> page,
                                                 @Param("pd") ProcessDefinition processDefinition);

In ProcessDefinition class, there is a filed: private ReleaseState releaseState.

It's an enum type, but in xml file, we compare it with String.

Brief change log

Delete the mybatis sentence that compares releaseState to an empty String.

Verify this pull request

This pull request is code cleanup without any test coverage.

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This pull request is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

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If your pull request contain incompatible change, you should also add it to docs/docs/en/guide/upgrede/incompatible.md

[ruanwenjun]

LGTM, there exist multiple place need to fix in ProcessDefinitionMapper, please modify these in this PR, and we need to add UT for this case.

[Mahongsheng]

I am trying to check this mapper and write unit tests. Please wait a minute.

[Mahongsheng]

I don't find any more bugs in ProcessDefinitionMapper. And I think I have completed the unit testings for this file. Please check. Salute.

[ruanwenjun]

Please fix the code style