Remove XOAUTH2 from Auto-Discovery SMTP auth feature #191

Job	Run time
Test with Codecov coverage (ubuntu-latest / 1.23)	58s
Dependency review	10s
Go vulnerabilities check	17s
golangci-lint (1.23)	30s
REUSE Compliance Check	13s
Test with SonarQube review (ubuntu-latest / 1.23)	1m 22s
Test on FreeBSD 14.0	2m 23s
Test on FreeBSD 13.4'	2m 46s
Test on FreeBSD 14.1	2m 19s
Test (macos-latest / 1.19)	32s
Test (macos-latest / 1.20)	37s
Test (macos-latest / 1.21)	27s
Test (macos-latest / 1.22)	22s
Test (macos-latest / 1.23)	23s
Test (ubuntu-latest / 1.19)	29s
Test (ubuntu-latest / 1.20)	28s
Test (ubuntu-latest / 1.23)	26s
Test (ubuntu-latest / 1.21)	25s
Test (ubuntu-latest / 1.22)	28s
Test (windows-latest / 1.19)	1m 13s
Test (windows-latest / 1.20)	2m 19s
Test (windows-latest / 1.22)	2m 6s
Test (windows-latest / 1.21)	2m 11s
Test (windows-latest / 1.23)	1m 52s
	25m 16s

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