Small size reduction and performance increase in the string duplicator.

FossilOrigin-Name: cda998f080cb00779d8c0d1c83d8fe2b74462cd4

src/malloc.c

@@ -726,9 +726,8 @@ char *sqlite3DbStrDup(sqlite3 *db, const char *z){
   if( z==0 ){
     return 0;
   }
-  n = sqlite3Strlen30(z) + 1;
-  assert( (n&0x7fffffff)==n );
-  zNew = sqlite3DbMallocRaw(db, (int)n);
+  n = strlen(z) + 1;
+  zNew = sqlite3DbMallocRaw(db, n);
   if( zNew ){
     memcpy(zNew, z, n);
   }