Remove jgitflow plugin from POM file

Use this script instead

```bash
GIT_USER_NAME=$(git config user.name)
GIT_USER_EMAIL=$(git config user.email)
git config user.name "iText Software (Community)"
git config user.email community@itextpdf.com

git checkout -b release/$RELEASE $COMMIT
find . -name pom.xml -o -name Version.java | \
    xargs sed -i 's/'$RELEASE'-SNAPSHOT/'$RELEASE'/'
find . -name pom.xml -o -name Version.java | \
    xargs git add
git commit \
    -m "[RELEASE] $RELEASE-SNAPSHOT -> $RELEASE"

git checkout develop
find . -name pom.xml -o -name Version.java | \
    xargs sed -i 's/'$RELEASE'-SNAPSHOT/'$DEVELOP'/'
find . -name pom.xml -o -name Version.java | \
    xargs git add
git commit \
    -m "[RELEASE] $RELEASE-SNAPSHOT -> $DEVELOP"

git checkout master
git merge release/$RELEASE \
    --no-ff \
    --log=$(git log --oneline master..release/$RELEASE | wc -l) \
    --stat \
    --signoff \
    -m "[RELEASE] iText 7 - $RELEASE" \
    -m "https://github.com/itext/itext7/releases/tag/$RELEASE"

MESSAGE_FILE=$(mktemp)
git log -1 --pretty=%B > $MESSAGE_FILE
git tag $RELEASE \
    -u D9EDD41A1AB17E4A2FE369D8035FD9539EE015A2 \
    -F $MESSAGE_FILE
rm -f $MESSAGE_FILE

git checkout develop
git merge %RELEASE \
    --no-ff \
    --strategy=recursive -X ours

git branch -D release/"$RELEASE"
```

Full script:
https://git.itextsupport.com/projects/QA/repos/release/browse/itext7/release.sh

Author: iText-CI

pom.xml

@@ -645,25 +645,6 @@
       <id>release</id>
       <build>
         <plugins>
-          <plugin>
-            <groupId>external.atlassian.jgitflow</groupId>
-            <artifactId>jgitflow-maven-plugin</artifactId>
-            <version>1.0-m5.1</version>
-            <configuration>
-              <!-- see goals wiki page for configuration options -->
-              <flowInitContext>
-                <masterBranchName>master</masterBranchName>
-                <developBranchName>develop</developBranchName>
-                <featureBranchPrefix>feature/</featureBranchPrefix>
-                <releaseBranchPrefix>release/</releaseBranchPrefix>
-                <hotfixBranchPrefix>hotfix/</hotfixBranchPrefix>
-                <versionTagPrefix />
-              </flowInitContext>
-              <allowUntracked>true</allowUntracked>
-              <autoVersionSubmodules>true</autoVersionSubmodules>
-              <updateDependencies>true</updateDependencies>
-            </configuration>
-          </plugin>
           <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-javadoc-plugin</artifactId>