tests/helper-runtests.sh

revlog: fix typo in 'buildtext' name

There are no such things as 'deltacomputer._buildtext'. I'm not sure why this
code never ran, but we better fix the typo.

#
# Avoid interference from actual test env:

unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL