Update contrib/linearize scripts to use the new .format() method

Summary: Avoid using % to format strings, switch to the new method instead.

Test Plan:

./src/bitcoind &

Create a config file called linearize.cfg with this content:

datadir=<your_data_dir>
max_height=10
hashlist=hashlist.txt
intput=<your_data_dir>/blocks
output_file=<some_path>/blockchain.dat

Then:

./contrib/linearize/linearize-hashes.py linearize.cfg > hashlist.txt

A file named hashlist.txt with 11 hashes should have been created.

./contrib/linearize/linearize-data.py linearize.cfg

A blockchain.dat file should be created under the path specified in the
configuration file.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2572