JBEHAVE-1585 Stop using deprecated parameter forkMode of Surefire p…

…lugin

`forkMode` parameter was deprecated in MavenSurefire plugin 2.14, and it was removed in 3.X.

The migration guide is available at: https://maven.apache.org/surefire-archives/surefire-2.22.2/maven-surefire-plugin/examples/fork-options-and-parallel-execution.html
The replacement for `forkMode=once` is `forkCount=1 (default), reuseForks=true (default)`.
Considering values are set by default, explicit configuration is omitted.

pom.xml

@@ -125,7 +125,6 @@
             <includes>
               <include>**/*Behaviour.java</include>
             </includes>
-            <forkMode>once</forkMode>
             <printSummary>true</printSummary>
             <useFile>true</useFile>
             <systemPropertyVariables>