refactor(test): refactor and delete redundant unit tests covered by main automation

[febyeji]

Summary

• Most tests are subsumed by the previous merges.
• Delete redundant unit tests covered by main automation

[tperami]

I think some of those test are hard to maintain and subsumed by existing CLI-level test and #103

In general, I think unit tests need to

• Only test small scale modules or functions that not reachable from the CLI
• Only exists if we do not have to update them (non-automatically) all the time (which we can't do for ounit tests)

Any test at an entire test level should be done from the CLI as it is easier to maintain and forces use to keep in sync the whole stack.

That means concretely:

• converter test is basically obsolete with CLI: tests: Add converter tests for all our test files #103
• assertion_test should only test direct assertion strings to AST (and should also test DNF conversion on simple examples). For example:

assert_parses_as "~(1:X0 = 1)"
           (Not (Atom (CmpCst (Reg (1, "X0"), Eq, Z.one))))

• ir_test and testrepr_test are just testing whole file parsing, even if looking at individual fields with this PR.
  they seem somewhat maintainable so I guess we can leave them as they are unless/until they become annoying later

Pretty printing round-trip tests are good: They mean we can reparse what was printed, however they are not really a "unit" test so we might want to move them later

[tperami]

Those tests were good, why are you removing them?

[tperami]

Those were good