(Sonar) Fix "Unused local variables should be removed" (#342)

## Remediation

This change fixes the following Sonar rule: "Unused local variables
should be removed" (id =
[java:S1481](https://rules.sonarsource.com/java/RSPEC-1481))

## Details

This change removes unused variables. Unused variables make the code
harder to read, which will lead to confusion and bugs. We only remove
variables that have no state-changing effects.

Our changes look something like this:

```diff
     catch (final UnsolvedSymbolException e) {
-      String errorMessage = "An unexpected exception happened";
       LOG.error("Problem resolving type of : {}", expr, e);
       return false;
     }
```

<details>
  <summary>More reading</summary>

*
[https://rules.sonarsource.com/java/RSPEC-1481/](https://rules.sonarsource.com/java/RSPEC-1481/)
</details>

I have additional improvements ready for this repo! If you want to see
them, leave the comment:
```
@pixeebot next
```
... and I will open a new PR right away!


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Author: pixeebot[bot]

plugins/codemodder-plugin-maven/src/main/java/io/codemodder/plugins/maven/operator/FormatCommand.java

@@ -267,7 +267,6 @@ private void parseXmlAndCharset(POMDocument pomFile) throws XMLStreamException,
     boolean mustTrack = false;
     boolean hasPreamble = false;
     int elementStart = 0;
-    int elementEnd = 0;
     List<XMLEvent> prevEvents = new ArrayList<>();
 
     while (eventReader.hasNext()) {