Remove code using a deprecated method

The `getRegisters()` method of `SDT` has been marked deprecated for a
long time, but has been kept in the code base as it is used in various
tests.  This commit makes the method private and removes (unused) code
in other classes that was calling this method.

This change shuts off two deprecation warnings from the linter.

Author: kostis

src/main/java/de/learnlib/ralib/oracles/mto/LabeledSDT.java

@@ -1,10 +1,8 @@
 package de.learnlib.ralib.oracles.mto;
 
-import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.Set;
 
 import de.learnlib.ralib.theory.SDT;
@@ -142,50 +140,4 @@ public static LabeledSDT pruneBranch(LabeledSDT lsdt, int label) {
 		return new LabeledSDT(lsdt, label);
 	}
 
-    @Override
-    public String toString() {
-        StringBuilder sb = new StringBuilder();
-        String regs = Arrays.toString(sdt.getRegisters().toArray());
-        sb.append(regs).append("-+\n");
-        toString(sb, spaces(regs.length()));
-        return sb.toString();
-    }
-
-    void toString(StringBuilder sb, String indentation) {
-    	if (sdt instanceof SDTLeaf) {
-    		sb.append(indentation).append("[Leaf").append(sdt.isAccepting() ? "+" : "-").append("]").append("\n");
-    	} else {
-	        LabeledSDT idioticSdt = this;
-	        sb.append(indentation).append("[]");
-	        final int childCount = idioticSdt.children.size();
-	        int count = 1;
-	        for (Entry<SDTGuard, LabeledSDT> e : idioticSdt.children.entrySet()) {
-	            SDTGuard g = e.getKey();
-	            String gString = g.toString();
-	            String nextIndent;
-	            if (count == childCount) {
-	                nextIndent = indentation + "      ";
-	            } else {
-	                nextIndent = indentation + " |    ";
-	            }
-
-	            if (count > 1) {
-	                sb.append(indentation).append(" +");
-	            }
-	            sb.append("- ").append(e.getValue().label).append(":").append(gString).append("\n");
-	            e.getValue().toString(sb, nextIndent);
-
-	            count++;
-	        }
-    	}
-    }
-
-    private String spaces(int max) {
-        StringBuilder sb = new StringBuilder();
-        for (int i = 0; i < max; i++) {
-            sb.append(" ");
-        }
-        return sb.toString();
-    }
-
 }

src/main/java/de/learnlib/ralib/theory/SDT.java

@@ -51,11 +51,11 @@ public SDT(Map<SDTGuard, SDT> children) {
      * @return
      */
     // todo: SDTs cannot have registers anymore, this should be data values!
-    // this method is currently only used in the toString methods of SDTs. Changing
-    // it will require changing many test cases as the toString methods are used
-    // to check the correctness of many SDTs.
+    // This private method is currently only used in the toString method of this
+    // class. Removing it will require changing many test cases as the toString
+    // method is used to check the correctness of many SDTs.
     @Deprecated
-    public Set<Register> getRegisters() {
+    private Set<Register> getRegisters() {
         Set<DataValue> temp = new LinkedHashSet<>();
         this.getVariables().stream().filter(SDTGuardElement::isDataValue).forEach((x) -> {
             temp.add((DataValue) x);

src/main/java/de/learnlib/ralib/theory/SDTLeaf.java

@@ -25,7 +25,6 @@
 
 import de.learnlib.ralib.data.SDTGuardElement;
 import de.learnlib.ralib.data.SDTRelabeling;
-import de.learnlib.ralib.data.SymbolicDataValue;
 
 /**
  * Leaf implementation of an SDT.
@@ -103,11 +102,6 @@ public Map<List<SDTGuard>, Boolean> getAllPaths(List<SDTGuard> path) {
     	return ret;
     }
 
-    @Override
-    public Set<SymbolicDataValue.Register> getRegisters() {
-        return new LinkedHashSet<>();
-    }
-
     @Override
     public Set<SDTGuardElement> getVariables() {
         return new LinkedHashSet<>();