Remove unused 'tls_load_default_certs' option

[FlorianVeaux]

This option isn't used yet and doesn't provide any value, there's no point in verifying the TLS connection if no CA is provided

[codecov]

Codecov Report

Merging #8013 (d3c2bf4) into master (5d58199) will increase coverage by 0.20%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
...tadog_checks_base/datadog_checks/base/utils/tls.py	91.54% <ø> (-0.12%)	⬇️
datadog_checks_base/tests/test_tls.py	100.00% <ø> (ø)
...atadog_checks_dev/datadog_checks/dev/structures.py	81.96% <0.00%> (-4.92%)	⬇️
couch/tests/test_couch.py
postgres/datadog_checks/postgres/util.py
mysql/datadog_checks/mysql/__about__.py
...server/datadog_checks/exchange_server/__about__.py
...tool/datadog_checks/cassandra_nodetool/__init__.py
couch/tests/conftest.py
mysql/tests/common.py
... and 136 more

[yzhan289]

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