Removing FilesSearch feature flag (#17548)

* Removing FilesSearch feature flag

* Fixing tests

* Adding an improvement on plain text extraction

* Adding tests for plain text extraction

* Removed unneeded conversion

* Adding missed license

* Remove the feature flag from the migration

* Fixing some tests

* Updating i18n/en.json file

app/file.go

@@ -782,7 +782,7 @@ func (a *App) UploadFileX(channelID, name string, input io.Reader,
 		}
 	}
 
-	if *a.Config().FileSettings.ExtractContent && a.Config().FeatureFlags.FilesSearch {
+	if *a.Config().FileSettings.ExtractContent {
 		infoCopy := *t.fileinfo
 		a.Srv().Go(func() {
 			err := a.ExtractContentFromFileInfo(&infoCopy)
@@ -1040,7 +1040,7 @@ func (a *App) DoUploadFileExpectModification(now time.Time, rawTeamId string, ra
 		}
 	}
 
-	if *a.Config().FileSettings.ExtractContent && a.Config().FeatureFlags.FilesSearch {
+	if *a.Config().FileSettings.ExtractContent {
 		infoCopy := *info
 		a.Srv().Go(func() {
 			err := a.ExtractContentFromFileInfo(&infoCopy)