`CCoinsViewCache::GetValueIn(…)` performs money summation like this:

```c++
CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
{
    if (tx.IsCoinBase())
        return 0;

    CAmount nResult = 0;
    for (unsigned int i = 0; i < tx.vin.size(); i++)
        nResult += AccessCoin(tx.vin[i].prevout).out.nValue;

    return nResult;
}
```

Note that no check is done to make sure that the resulting `nResult` is such that it stays within the money bounds (`MoneyRange(nResult)`), or that the summation does not trigger a signed integer overflow.

Proof of concept output:

```
coins.cpp:243:17: runtime error: signed integer overflow: 9223200000000000000 + 2100000000000000 cannot be represented in type 'long'
GetValueIn = -9221444073709551616
```

Proof of concept code:

```c++
CMutableTransaction mutable_transaction;
mutable_transaction.vin.resize(4393);

Coin coin;
coin.out.nValue = MAX_MONEY;
assert(MoneyRange(coin.out.nValue));

CCoinsCacheEntry coins_cache_entry;
coins_cache_entry.coin = coin;
coins_cache_entry.flags = CCoinsCacheEntry::DIRTY;

CCoinsView backend_coins_view;
CCoinsViewCache coins_view_cache{&backend_coins_view};
CCoinsMap coins_map;
coins_map.emplace(COutPoint{}, std::move(coins_cache_entry));
coins_view_cache.BatchWrite(coins_map, {});

const CAmount total_value_in = coins_view_cache.GetValueIn(CTransaction{mutable_transaction});
std::cout << "GetValueIn = " << total_value_in << std::endl;
```

As far as I can tell `CCoinsViewCache::GetValueIn` is unused outside of tests:

```sh
$ git grep GetValueIn ":(exclude)src/test/" ":(exclude)src/bench/"
src/coins.cpp:CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
src/coins.h:    CAmount GetValueIn(const CTransaction& tx) const;
src/primitives/transaction.h:    // GetValueIn() is a method on CCoinsViewCache, because
```

I suggest we drop the unused `CCoinsViewCache::GetValueIn(…)`.

Any objections? :)
{
    
    unsigned char ch[] = {0x01, 0x00, 0x00, 0x00, 0x01, 0x6b, 0xff, 0x7f, 0xcd, 0x4f, 0x85, 0x65, 0xef, 0x40, 0x6d, 0xd5, 0xd6, 0x3d, 0x4f, 0xf9, 0x4f, 0x31, 0x8f, 0xe8, 0x20, 0x27, 0xfd, 0x4d, 0xc4, 0x51, 0xb0, 0x44, 0x74, 0x01, 0x9f, 0x74, 0xb4, 0x00, 0x00, 0x00, 0x00, 0x8c, 0x49, 0x30, 0x46, 0x02, 0x21, 0x00, 0xda, 0x0d, 0xc6, 0xae, 0xce, 0xfe, 0x1e, 0x06, 0xef, 0xdf, 0x05, 0x77, 0x37, 0x57, 0xde, 0xb1, 0x68, 0x82, 0x09, 0x30, 0xe3, 0xb0, 0xd0, 0x3f, 0x46, 0xf5, 0xfc, 0xf1, 0x50, 0xbf, 0x99, 0x0c, 0x02, 0x21, 0x00, 0xd2, 0x5b, 0x5c, 0x87, 0x04, 0x00, 0x76, 0xe4, 0xf2, 0x53, 0xf8, 0x26, 0x2e, 0x76, 0x3e, 0x2d, 0xd5, 0x1e, 0x7f, 0xf0, 0xbe, 0x15, 0x77, 0x27, 0xc4, 0xbc, 0x42, 0x80, 0x7f, 0x17, 0xbd, 0x39, 0x01, 0x41, 0x04, 0xe6, 0xc2, 0x6e, 0xf6, 0x7d, 0xc6, 0x10, 0xd2, 0xcd, 0x19, 0x24, 0x84, 0x78, 0x9a, 0x6c, 0xf9, 0xae, 0xa9, 0x93, 0x0b, 0x94, 0x4b, 0x7e, 0x2d, 0xb5, 0x34, 0x2b, 0x9d, 0x9e, 0x5b, 0x9f, 0xf7, 0x9a, 0xff, 0x9a, 0x2e, 0xe1, 0x97, 0x8d, 0xd7, 0xfd, 0x01, 0xdf, 0xc5, 0x22, 0xee, 0x02, 0x28, 0x3d, 0x3b, 0x06, 0xa9, 0xd0, 0x3a, 0xcf, 0x80, 0x96, 0x96, 0x8d, 0x7d, 0xbb, 0x0f, 0x91, 0x78, 0xff, 0xff, 0xff, 0xff, 0x02, 0x8b, 0xa7, 0x94, 0x0e, 0x00, 0x00, 0x00, 0x00, 0x19, 0x76, 0xa9, 0x14, 0xba, 0xde, 0xec, 0xfd, 0xef, 0x05, 0x07, 0x24, 0x7f, 0xc8, 0xf7, 0x42, 0x41, 0xd7, 0x3b, 0xc0, 0x39, 0x97, 0x2d, 0x7b, 0x88, 0xac, 0x40, 0x94, 0xa8, 0x02, 0x00, 0x00, 0x00, 0x00, 0x19, 0x76, 0xa9, 0x14, 0xc1, 0x09, 0x32, 0x48, 0x3f, 0xec, 0x93, 0xed, 0x51, 0xf5, 0xfe, 0x95, 0xe7, 0x25, 0x59, 0xf2, 0xcc, 0x70, 0x43, 0xf9, 0x88, 0xac, 0x00, 0x00, 0x00, 0x00, 0x00};
    std::vector<unsigned char> vch(ch, ch + sizeof(ch) -1);
    CDataStream stream(vch, SER_DISK, CLIENT_VERSION);
    CMutableTransaction tx;
    stream >> tx;
    TxValidationState state;
    BOOST_CHECK_MESSAGE(CheckTransaction(CTransaction(tx), state) && state.IsValid(), "Simple deserialized transaction should be valid.");
    
    tx.vin.push_back(tx.vin[0]);
    BOOST_CHECK_MESSAGE(!CheckTransaction(CTransaction(tx), state) || !state.IsValid(), "Transaction with duplicate txins should be invalid.");
}
BOOST_AUTO_TEST_CASE(test_Get)