cpufreq: interactive_pro: Fix double definition of get_cpu_idle_time()

Upstream has moved get_cpu_idle_time() and related functions into core
CPUfreq framework. Remove unnecessary functions in interactive governor.

Change-Id: Ibba09e190581610b2c4bc17344164973414f1b12
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>