8332597: Remove redundant methods from j.l.classfile.ClassReader API

Reviewed-by: liach, jlahoda

src/java.base/share/classes/java/lang/classfile/ClassReader.java

@@ -71,22 +71,9 @@ public sealed interface ClassReader extends ConstantPool
     /** {@return the constant pool entry describing the name of the superclass, if any} */
     Optional<ClassEntry> superclassEntry();
 
-    /** {@return the offset into the classfile of the {@code this_class} field} */
-    int thisClassPos();
-
     /** {@return the length of the classfile, in bytes} */
     int classfileLength();
 
-    // Buffer related
-
-    /**
-     * {@return the offset following the block of attributes starting at the
-     * specified position}
-     * @param offset the offset into the classfile at which the attribute block
-     *               starts
-     */
-    int skipAttributeHolder(int offset);
-
     // Constant pool
 
     /**