tests: Don't override tick rate in Ruby tests

tests: Don't override tick rate in Ruby tests

Most Ruby tests assume that the highest frequency in the system under
test is 1GHz and limits the global tick rate to this frequency. This
assumption is broken since the default Ruby configuration scripts
clock the CPU at 2Ghz, which results in warnings and sometimes
incorrect behaviour.

Change-Id: I4b204660862ce3b0ea4a13df42caacd4398fef8c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15975
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>