[ntcore] Remove NT3 support (#7625)

- Remove StartClient3
- Rename StartClient4 to StartClient
- Remove port3 parameter from StartServer
- Remove 3-suffix constants
- Remove 4 suffix from constants

Also remove Shuffleboard build from CI.

cameraserver/multiCameraServer/src/main/java/edu/wpi/Main.java

@@ -176,7 +176,7 @@ public final class Main {
     } else {
       System.out.println("Setting up NetworkTables client for team " + team);
       ntinst.setServerTeam(team);
-      ntinst.startClient4("multicameraserver");
+      ntinst.startClient("multicameraserver");
     }
 
     // start cameras

cameraserver/multiCameraServer/src/main/native/cpp/main.cpp

@@ -190,7 +190,7 @@ int main(int argc, char* argv[]) {
     ntinst.StartServer();
   } else {
     wpi::print("Setting up NetworkTables client for team {}\n", team);
-    ntinst.StartClient4("multicameraserver");
+    ntinst.StartClient("multicameraserver");
     ntinst.SetServerTeam(team);
   }