Fix package plainbox-provider-pc-sanity build fail (bugfix)

[cyruslien]

edid_continuous_frequency_check.py:

• Remove unused glob module

Description

plainbox-provider-pc-sanity build failed due to flake8 found unused module glob in edid_continuous_frequency_check.py.
Build log:

python3 contrib/pc-sanity/manage.py test
.....................................................................................................F..
======================================================================
FAIL: test_flake8_/<<PKGBUILDDIR>>/contrib/pc-sanity/bin/edid_continuous_frequency_check.py (plainbox.provider_manager.Flake8Tests.test_flake8_/<<PKGBUILDDIR>>/contrib/pc-sanity/bin/edid_continuous_frequency_check.py)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/plainbox/provider_manager.py", line 1605, in _test
    self.fail(failure_reason)
AssertionError: /<<PKGBUILDDIR>>/contrib/pc-sanity/bin/edid_continuous_frequency_check.py:5:1: F401 'glob' imported but unused

Resolved issues

https://warthogs.atlassian.net/browse/SOMERVILLE-2215

Documentation

None

Tests

$ flake8 --count contrib/pc-sanity/bin/edid_continuous_frequency_check.py 
0

[KaiChuan-Hsieh]

LGTM