Move methods from others to correct packages (#6475)

refactor: Move methods from `others` package to their respective packages

src/main/java/com/thealgorithms/strings/RemoveDuplicateFromString.java

@@ -0,0 +1,30 @@
+package com.thealgorithms.strings;
+
+/**
+ * @author Varun Upadhyay (https://github.com/varunu28)
+ */
+public final class RemoveDuplicateFromString {
+    private RemoveDuplicateFromString() {
+    }
+
+    /**
+     * Removes duplicate characters from the given string.
+     *
+     * @param input The input string from which duplicate characters need to be removed.
+     * @return A string containing only unique characters from the input, in their original order.
+     */
+    public static String removeDuplicate(String input) {
+        if (input == null || input.isEmpty()) {
+            return input;
+        }
+
+        StringBuilder uniqueChars = new StringBuilder();
+        for (char c : input.toCharArray()) {
+            if (uniqueChars.indexOf(String.valueOf(c)) == -1) {
+                uniqueChars.append(c); // Append character if it's not already in the StringBuilder
+            }
+        }
+
+        return uniqueChars.toString();
+    }
+}