Fix for bug introduced in backporting MPI MSVC fix

Some variables were being declared twice in int_div_int() due to an error in
cherry-picking the commit from mbedtls-1.3

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index 15457ab..85514a3 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1127,10 +1127,6 @@
 
     return (t_uint) quotient;
 #else
-    const t_uint radix = 1 << biH;
-    t_uint d0, d1, q0, q1, rAX, r0, quotient;
-    t_uint u0_msw, u0_lsw;
-    int s;
 
     /*
      * Algorithm D, Section 4.3.1 - The Art of Computer Programming