Remove org.scijava.usage package

The gathering of usage statistics is too contentions a topic to be
located in SJC.

Author: hinerm

src/main/java/org/scijava/AbstractGateway.java

@@ -60,7 +60,6 @@
 import org.scijava.thread.ThreadService;
 import org.scijava.tool.IconService;
 import org.scijava.tool.ToolService;
-import org.scijava.usage.UsageService;
 import org.scijava.widget.WidgetService;
 
 /**
@@ -223,11 +222,6 @@ public ToolService tool() {
 		return get(ToolService.class);
 	}
 
-	@Override
-	public UsageService usage() {
-		return get(UsageService.class);
-	}
-
 	@Override
 	public WidgetService widget() {
 		return get(WidgetService.class);

src/main/java/org/scijava/Gateway.java

@@ -58,7 +58,6 @@
 import org.scijava.thread.ThreadService;
 import org.scijava.tool.IconService;
 import org.scijava.tool.ToolService;
-import org.scijava.usage.UsageService;
 import org.scijava.widget.WidgetService;
 
 /**
@@ -190,8 +189,6 @@ public interface Gateway extends RichPlugin, Versioned {
 
 	ToolService tool();
 
-	UsageService usage();
-
 	WidgetService widget();
 
 	// -- Gateway methods - application --

src/main/java/org/scijava/usage/DefaultUsageService.java

@@ -95,7 +95,6 @@ public void testFull() {
 				org.scijava.tool.DefaultToolService.class,
 				org.scijava.ui.DefaultUIService.class,
 				org.scijava.ui.dnd.DefaultDragAndDropService.class,
-				org.scijava.usage.DefaultUsageService.class,
 				org.scijava.welcome.DefaultWelcomeService.class,
 				org.scijava.widget.DefaultWidgetService.class,
 				org.scijava.log.StderrLogService.class,