Missing `bdb` argument in `implicit_reference_var_colno_exp` in `compiler.py` will cause RuntimeError

[fsaad]

https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1077-L1078
https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1093-L1094
https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1147-L1148
https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1264-L1265
https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1324-L1325
https://github.com/probcomp/bayeslite/blob/master/src/compiler.py#L1433-L1434

Thank you pylint in sublime gutter.

Strange that no clients or test cases execute this code path.

[fsaad]

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