Build MobilityFlink without a warning

[estebanzimanyi]

MeosSetSetJoin, in the binding and the benchmark modules, frees the index pairs MEOS returns
through com.kenai.jffi.MemoryIO.freeMemory, which calls the system free MEOS allocates with. jffi
is the native layer jnr-ffi runs on, so it shares the classloader of every MEOS call inside the
engine, and MobilityFlink calls no internal JDK API.

benchmark/pom.xml declares junit-jupiter-api once, at junit.jupiter.version, the 5.8.2 Maven
resolves already; the second declaration, at 5.7.0, is gone.

The Maven workflow refuses a build that prints a warning: a [WARNING] line from Maven or a
WARNING: line from JUnit or the JVM during the tests.

Measured. Against MobilityDB 85ad3e2891, the catalog of MEOS-API 1c50d3611a and the generator and
jar of JMEOS main 52432a1d, whose Flink runtimes free their values through jffi, mvn clean test under Maven 3.9.16 prints no warning line and the 18 and 12 tests pass. Main
prints twenty: twelve sun.misc.Unsafe in the two MeosSetSetJoin and the eight lines Maven prints
for the duplicate junit-jupiter-api in the benchmark model.