[P4Testgen] Move p4tools.def to common/ir.def, introduce a hashing function for state and symbolic variables.

[fruffy]

Remove one more piece of boost in the compiler.

This time we replace some boost containers with Abseil flat maps and sets. For that to work we needed to introduce hashers and comparison function for some of the special P4Tools variables. We also need custom comparators and hashers because we only want to compare the labels and names of the variables, not the types. The hashers use hash_combine from our hash utilities.

Also fix a small code in the Python PTF scripts that led to spurious failures (trying to remove a log file that was already removed).