Don't use onloadable things in remoting mkdirs calls.

mkdirs do remoting call by creating anonymous class.
Remoting on remote side must load outer FilePath class with imports.
FilePath had SystemProperties OnMaster.

core/src/main/java/hudson/FilePath.java

@@ -106,7 +106,6 @@ import jenkins.SoloFilePathFilter;
 import jenkins.model.Jenkins;
 import jenkins.security.MasterToSlaveCallable;
 import jenkins.util.ContextResettingExecutorService;
-import jenkins.util.SystemProperties;
 import jenkins.util.VirtualFile;
 import org.apache.commons.compress.archivers.tar.TarArchiveEntry;
 import org.apache.commons.compress.archivers.tar.TarArchiveInputStream;
@@ -2371,7 +2370,7 @@ public final class FilePath implements Serializable {
      * Default bound for {@link #validateAntFileMask(String, int, boolean)}.
      * @since 1.592
      */
-    public static int VALIDATE_ANT_FILE_MASK_BOUND = SystemProperties.getInteger(FilePath.class.getName() + ".VALIDATE_ANT_FILE_MASK_BOUND", 10000);
+    public static int VALIDATE_ANT_FILE_MASK_BOUND = Integer.getInteger(FilePath.class.getName() + ".VALIDATE_ANT_FILE_MASK_BOUND", 10000);
 
     /**
      * Like {@link #validateAntFileMask(String)} but performing only a bounded number of operations.