Upgrade JNA to 5.6.0

Also remove remaining comments/doc referencing `-Dcassandra.boot_without_jna`

 patch by Adrain Cole, Mick Semb Wever; reviewed by Benjamin Lerer, Joey Lynch for CASSANDRA-16212

Co-authored-by: Adrian Cole <adrian.f.cole@gmail.com>

NEWS.txt

@@ -254,6 +254,8 @@ Upgrading
       default (16) was meant for spinning disk volumes.  See CASSANDRA-14902 for details.
     - Custom compaction strategies must now handle getting sstables added/removed notifications for
       sstables already added/removed - see CASSANDRA-14103 for details.
+    - Support for JNA with glibc 2.6 and earlier has been removed. Centos 5, Debian 4, and Ubuntu 7.10 operating systems
+      must be first upgraded. See CASSANDRA-16212 for more.
 
 
 Deprecation

build.xml

@@ -607,7 +607,7 @@
             <exclusion groupId="asm" artifactId="asm"/> <!-- this is the outdated version 3.1 -->
             <exclusion groupId="org.slf4j" artifactId="slf4j-api"/>
           </dependency>
-          <dependency groupId="net.java.dev.jna" artifactId="jna" version="4.2.2"/>
+          <dependency groupId="net.java.dev.jna" artifactId="jna" version="5.6.0"/>
 
           <dependency groupId="org.jacoco" artifactId="org.jacoco.agent" version="${jacoco.version}"/>
           <dependency groupId="org.jacoco" artifactId="org.jacoco.ant" version="${jacoco.version}"/>

doc/source/configuration/cass_env_sh_file.rst

@@ -18,10 +18,6 @@ Facilitates setting auto_bootstrap to false on initial set-up of the cluster. Th
 ---------------------------------------------------------
 In a multi-instance deployment, multiple Cassandra instances will independently assume that all CPU processors are available to it. This setting allows you to specify a smaller set of processors.
 
-``cassandra.boot_without_jna=true``
------------------------------------
-If JNA fails to initialize, Cassandra fails to boot. Use this command to boot Cassandra without JNA.
-
 ``cassandra.config=<directory>``
 --------------------------------
 The directory location of the ``cassandra.yaml file``. The default location depends on the type of installation.

src/java/org/apache/cassandra/service/StartupCheck.java

@@ -25,8 +25,7 @@ import org.apache.cassandra.exceptions.StartupException;
  * information or advice on tuning and non-fatal environmental issues (e.g. like
  * checking for and warning about suboptimal JVM settings).
  * Other checks may indicate that they system is not in a correct state to be started.
- * Examples include inability to load JNA when the cassandra.boot_without_jna option
- * is not set, missing or unaccessible data directories, unreadable sstables and
+ * Examples include missing or unaccessible data directories, unreadable sstables and
  * misconfiguration of cluster_name in cassandra.yaml.
  *
  * The StartupChecks class manages a collection of these tests, which it executes