Use Jenkins.get() instead of deprecated method and minor improvements

[StefanSpieker]

Use Jenkins.get() instead of deprecated method and minor improvements:

• Use StandardCharsets.UTF_8
• removed unused imports

Testing done

All tests passed. Jenkins came up normally in debug environment.

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6. Ensure you have provided tests - that demonstrates feature works or fixes the issue

[halkeye]

Do you know when get was added? Is it newer than the base version in the pom?

[StefanSpieker]

Since 2.98 Jenkins.java which is a lot older than 2.235.5

[halkeye]

Oh wow I updated it to 2.x at some point. I thought it was still in the 1s. Okay I'll take a poke