Merge #11838: qa: Add getrawtransaction in_active_chain=False test

Summary:
fa4c16d qa: Add getrawtransaction in_active_chain=False test (MarcoFalke)

Pull request description:

#10275 accidentally forgot to add a test for `in_active_chain==False`.

This adds a test and also removes the special casing of `blockhash.IsNull()`, which makes no sense imo.

Tree-SHA512: 6c51295820b3dcd53b0b48020ab2b8c8f5864cd5061ddab2b35d35d643eb3e60ef95ff20c06c985a2e47f7080e82f27f3e00ee61c85dce627776d5ea6febee8f

Backport of Core PR 11838
https://github.com/bitcoin/bitcoin/pull/11838/files
Completes T593

Test Plan:
make check
test_runner.py rpc_rawtransaction

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D2801