Remove unnecessary files in third_party/bigint

third_party/bigint/BigIntegerAlgorithms.hh

-#ifndef BIGINTEGERALGORITHMS_H
-#define BIGINTEGERALGORITHMS_H
-
-#include "BigInteger.hh"
-
-/* Some mathematical algorithms for big integers.
- * This code is new and, as such, experimental. */
-
-// Returns the greatest common divisor of a and b.
-BigUnsigned gcd(BigUnsigned a, BigUnsigned b);
-
-/* Extended Euclidean algorithm.
- * Given m and n, finds gcd g and numbers r, s such that r*m + s*n == g. */
-void extendedEuclidean(BigInteger m, BigInteger n,
-                BigInteger &g, BigInteger &r, BigInteger &s);
-
-/* Returns the multiplicative inverse of x modulo n, or throws an exception if
- * they have a common factor. */
-BigUnsigned modinv(const BigInteger &x, const BigUnsigned &n);
-
-// Returns (base ^ exponent) % modulus.
-BigUnsigned modexp(const BigInteger &base, const BigUnsigned &exponent,
-                const BigUnsigned &modulus);
-
-#endif