fix: remove redundant main method to resolve PMD violation

Author: polasisubash

src/main/java/com/thealgorithms/ciphers/ElGamalCipher.java

@@ -34,3 +34,4 @@ public BigInteger decrypt(BigInteger c1, BigInteger c2) {
         BigInteger sInv = s.modInverse(p);
         return c2.multiply(sInv).mod(p);
     }
+}