Technical debt/Unused config

For the script that detects unused variables in wmf-config, see https://gist.github.com/Krinkle/15be368abdbf918c8ef7a06cde011457.

Resolved items are removed in batches. See prior work at one, two, …

Results as of Thu 2020-05-28 13:22:46 -0700 with operations/mediawiki-config.git at 4aec190e227d2ed3e4332282cb2cb347e491a669:

Param	Filename	Component	Status
ArticlePlaceholderSearchIntegrationBackend	InitialiseSettings.php
BabelCentralApi	CommonSettings.php
CentralAuthAutoNew	CommonSettings.php
CentralAuthUseSlaves	CommonSettings-labs.php CommonSettings.php
CirrusSimilarityProfiles	InitialiseSettings.php
FlowMaintenanceMode	CommonSettings.php
LDAPLowerCaseUsernameScheme	wikitech.php
LDAPUseFetchedUsername	wikitech.php
LanguageCodeHasNotBeenSet	tests/multiversion/StaticSettingsGenerationTest.php
MFAppPackageId	InitialiseSettings.php
MFExperiments	InitialiseSettings.php
MFLazyLoadReferences	InitialiseSettings.php
MFPhotoUploadEndpoint	tests/multiversion/StaticSettingsTest.php InitialiseSettings-labs.php
MinervaShowShareButton	InitialiseSettings-labs.php
NoticeFundraisingUrl	CommonSettings.php
NotificationSenderName	CommonSettings.php
QuickSurveysRequireHttps	CommonSettings-labs.php
RelatedArticlesLoggingBucketSize	CommonSettings.php
RestrictionMethod	CommonSettings.php
TranslateClustersAndMirrors	CommonSettings.php
UseContributionTracking	CommonSettings.php InitialiseSettings.php
WBCSDefaultPrefixRescoreProfile	SearchSettingsForWikidata.php
WBCSEnableDispatchingQueryBuilder	SearchSettingsForSDC.php
WBCSFulltextSearchProfile	SearchSettingsForWikidata.php
WBCSFulltextSearchProfiles	SearchSettingsForWikidata.php
WBCSPrefixSearchProfiles	SearchSettingsForWikidata.php
WBCSRescoreFunctionChains	SearchSettingsForWikidata.php
WBCSRescoreProfiles	SearchSettingsForWikidata.php
WMEPhp7SamplingRate	CommonSettings.php
WMEPrintEnabled	InitialiseSettings.php
WMEPrintSamplingRate	InitialiseSettings.php