Don't check apex_available for host

The check doesn't make sense for host.

Test: ALLOW_MISSING_DEPENDENCIES=true DIST_DIR=out/dist
./art/tools/dist_linux_bionic.sh -j110 com.android.art.host
is successful

Change-Id: Icdb4bb557a83b3c8044e6c73721dab47c56888a1

apex/apex.go

@@ -1191,6 +1191,7 @@ func (a *apexBundle) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	})
 
 	// check apex_available requirements
+	if !ctx.Host() {
 		for _, fi := range filesInfo {
 			if am, ok := fi.module.(android.ApexModule); ok {
 				if !am.AvailableFor(ctx.ModuleName()) {
@@ -1199,6 +1200,7 @@ func (a *apexBundle) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 				}
 			}
 		}
+	}
 
 	// prepend the name of this APEX to the module names. These names will be the names of
 	// modules that will be defined if the APEX is flattened.