clean up script_tests -- move segwit recovery into static json

Summary:
The script_build generated tests in script_tests are best reserved for
those tests that have transaction signatures in them -- they may need to
be regenerated for some reason as they are sensitive to transaction
contents and hashtype. Though non-signature tests can be done this way,
they unnecessarily add to the (quite large) computational resources used
during script_tests.cpp compilation and cause a warning during build:
variable tracking size limit exceeded with -fvar-tracking-assignments, retrying without

Since segwit recovery tests involve no signatures, they can be moved into
the static parts of the json file.

Test Plan: make check

Reviewers: deadalnix, Mengerian, florian, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3416