[6.15.z] remove no_proxy default check in /etc/virt-who.conf

[Satellite-QE]

Cherrypick of PR: #15592

Problem Statement

As the default no_proxy is not enabled in /etc/virt-who.conf , if the no_proxy is not set, it will also not enable in /etc/virt-who.conf , so remove the default check
[system_environment]
#http_proxy=
#https_proxy=
#no_proxy=

Test Cases: PASS

(robottelo_vv_master) [root@dell-per740-68-vm-05 robottelo]# pytest ./tests/foreman/virtwho/api/test_esx_sca.py -k test_positive_proxy_option --disable-pytest-warnings -q
.                                                                                                                                                                                                           [100%]
1 passed, 12 deselected, 3 warnings in 174.34s (0:02:54)