Remove non-cost global variables from the tests

[odow]

The tests use a lot of non-const global variables: https://github.com/lanl-ansi/Juniper.jl/blob/df63a8d41b699be47d1eeecacef3ec2a6572c0e4/test/runtests.jl#L43-L47 I wonder if that's a reason why the tests take so long to run