scripted-diff: Use randbits/bool instead of randrange where possible

Summary:
As per Pieter Wuille' work.

-BEGIN VERIFY SCRIPT-
sed -i 's/insecure_randbits(1)/insecure_randbool()/g' src/test/*_tests.cpp
sed -i 's/insecure_randrange(2)/insecure_randbool()/g' src/test/*_tests.cpp
sed -i 's/insecure_randrange(4)/insecure_randbits(2)/g' src/test/*_tests.cpp
sed -i 's/insecure_randrange(32)/insecure_randbits(5)/g' src/test/*_tests.cpp
sed -i 's/insecure_randrange(256)/insecure_randbits(8)/g' src/test/*_tests.cpp
-END VERIFY SCRIPT-

Test Plan:

make check

Reviewers: schancel, #bitcoin_abc

Reviewed By: schancel, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D890