Big Five Warnings from AFQMC

I get many of these from clang, they are annoying. Please fix or if you must push a suppression of your warning in your headers, see Utilities/BoostRandom.h if you don't undestand me.
```shell
In file included from ../src/AFQMC/Walkers/WalkerSet.hpp:16:
../src/AFQMC/Walkers/SerialWalkerSet.hpp:68:20: warning: explicitly defaulted move assignment operator is implicitly de\
leted [-Wdefaulted-function-deleted]
SerialWalkerSet& operator=(SerialWalkerSet&& other) = default;
^
../src/AFQMC/Walkers/SerialWalkerSet.hpp:43:24: note: move assignment operator of 'SerialWalkerSet' is implicitly delet\
ed because base class 'WalkerSetBase, device_ptr >' (aka 'WalkerSetBase >, std::complex *>') has a deleted move assi\
gnment operator
class SerialWalkerSet: public WalkerSetBase,
^
../src/AFQMC/Walkers/WalkerSetBase.h:108:18: note: 'operator=' has been explicitly marked deleted here
WalkerSetBase& operator=(WalkerSetBase const& other) = delete;
^
```