Remove shared VM memory so tests can run concurrently

[deelawn]

There is a shared memory issue when trying to run multiple txtar tests that start a gnoland node. The goal is to remove this limitation and roll back the changes in PR #1342 that changes them to run serially in order to avoid the shared memory issue. The serial solution will not continue to be sustainable as more tests are added.

[thehowl]

rg -t go '^var' gnovm :)

probably the most important one is var preprocessing in preprocess.go