gitweb: Time::HiRes is in core for Perl 5.8

We say 'use 5.008' at the beginning of the script, therefore there is no
need to check if Time::HiRes module is available.  We can also import
gettimeofday and tv_interval.

Signed-off-by: Jakub Narebski <redacted>
Signed-off-by: Junio C Hamano <redacted>