Cleanup of code

[kamilkrzywanski]

There are lots of warnings at IJ. I fixed some of them.

[skybber]

Good job , Thanks !

[skybber]

HA build is broken now:

mvn clean package -Dmaven.test.skip=true

is failing on:

[INFO] Recompiling the module because of changed dependency.
[INFO] Compiling 23 source files with javac [debug release 11] to target/classes
[INFO] /home/lada/workspaces/workspace-ha/HotswapAgent/plugin/hotswap-agent-proxy-plugin/src/main/java/org/hotswap/agent/plugin/proxy/java/ProxyGenerator.java: /home/lada/workspaces/workspace-ha/HotswapAgent/plugin/hotswap-agent-proxy-plugin/src/main/java/org/hotswap/agent/plugin/proxy/java/ProxyGenerator.java uses or overrides a deprecated API.
[INFO] /home/lada/workspaces/workspace-ha/HotswapAgent/plugin/hotswap-agent-proxy-plugin/src/main/java/org/hotswap/agent/plugin/proxy/java/ProxyGenerator.java: Recompile with -Xlint:deprecation for details.
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] /home/lada/workspaces/workspace-ha/HotswapAgent/plugin/hotswap-agent-proxy-plugin/src/main/java/org/hotswap/agent/plugin/proxy/java/ProxyGenerator.java:[46,20] package sun.security.action is not visible
  (package sun.security.action is declared in module java.base, which does not export it to the unnamed module)
[INFO] 1 error

[kamilkrzywanski]

@skybber Probably not caused by these commits, rather by 8400633.
While cherry-picking, I missed removing <maven.compiler.release>11</maven.compiler.release> from 0e3fa16.