spindle_logd does not delete heap allocations

Nobody has claimed this yet.

### Bug:
`MsgReader` allocates a new connection onto the heap but delete is never called on the connection

Allocation:
https://github.com/llnl/Spindle/blob/585dacff6734eb039d318577711d47c5b950699c/src/logging/spindle_logd.cc#L408

#### Connection cleanup

Only removes the connection from the map:
https://github.com/llnl/Spindle/blob/585dacff6734eb039d318577711d47c5b950699c/src/logging/spindle_logd.cc#L476-L478

Only closes the file descriptor and clears the map:
https://github.com/llnl/Spindle/blob/585dacff6734eb039d318577711d47c5b950699c/src/logging/spindle_logd.cc#L594-L600

### Fix:
Two options:

```
for (std::map::iterator i = conns.begin(); i != conns.end(); i++) {
if (i->second->shutdown) {
delete i->second;
conns.erase(i);
```

```
~MsgReader()
{
for (std::map::iterator i = conns.begin(); i != conns.end(); i++) {
int fd = i->first;
close(fd);
delete i->second;
}
conns.clear();
```

Or swap to an `std::unique_ptr`:
```
std::map> conns;
...
Connection *con = std::make_unique();
```

Read src/logging/spindle_logd.cc at the MsgReader allocation and the connection cleanup paths around lines 476-478 and 594-600. Trace how Connection objects are stored and removed, then verify that shutdown and individual connection cleanup release each allocation without invalidating the map iteration.

Written by the indexing model from the issue text.