[Synthetics] Remove dead code (elastic#193335)

## Summary

Gets rid of unused files and some types, constants, etc. that are no
longer referenced in production code.

(cherry picked from commit d4ee1ca)

x-pack/plugins/observability_solution/synthetics/common/translations/translations.ts

@@ -7,18 +7,6 @@
 
 import { i18n } from '@kbn/i18n';
 
-export const URL_LABEL = i18n.translate('xpack.synthetics.monitorList.table.url.name', {
-  defaultMessage: 'Url',
-});
-
-export const TAGS_LABEL = i18n.translate('xpack.synthetics.monitorList.table.tags.name', {
-  defaultMessage: 'Tags',
-});
-
-export const PROJECT_LABEL = i18n.translate('xpack.synthetics.monitorList.table.project.name', {
-  defaultMessage: 'Project ID',
-});
-
 export const STATUS_UP_LABEL = i18n.translate('xpack.synthetics.monitorList.statusColumn.upLabel', {
   defaultMessage: 'Up',
 });
@@ -29,29 +17,3 @@ export const STATUS_DOWN_LABEL = i18n.translate(
     defaultMessage: 'Down',
   }
 );
-
-export const STATUS_COMPLETE_LABEL = i18n.translate(
-  'xpack.synthetics.monitorList.statusColumn.completeLabel',
-  {
-    defaultMessage: 'Complete',
-  }
-);
-
-export const STATUS_FAILED_LABEL = i18n.translate(
-  'xpack.synthetics.monitorList.statusColumn.failedLabel',
-  {
-    defaultMessage: 'Failed',
-  }
-);
-
-export const SECONDS_LABEL = i18n.translate('xpack.synthetics.seconds.label', {
-  defaultMessage: 'seconds',
-});
-
-export const SEC_LABEL = i18n.translate('xpack.synthetics.seconds.shortForm.label', {
-  defaultMessage: 'sec',
-});
-
-export const MS_LABEL = i18n.translate('xpack.synthetics.millisecond.abbreviation.label', {
-  defaultMessage: 'ms',
-});

x-pack/plugins/observability_solution/synthetics/public/apps/synthetics/components/certificates/index.ts

@@ -5,8 +5,11 @@
  * 2.0.
  */
 
+export * from './cert_refresh_btn';
 export * from './cert_monitors';
 export * from './cert_search';
 export * from './cert_status';
+export * from './certificates';
 export * from './certificates_list';
+export * from './certificate_title';
 export * from './fingerprint_col';

x-pack/plugins/observability_solution/synthetics/public/apps/synthetics/components/getting_started/simple_monitor_form.tsx

@@ -119,13 +119,6 @@ export const WEBSITE_URL_LABEL = i18n.translate(
   }
 );
 
-export const WEBSITE_URL_PLACEHOLDER = i18n.translate(
-  'xpack.synthetics.monitorManagement.websiteUrlPlaceholder',
-  {
-    defaultMessage: 'Enter a website URL',
-  }
-);
-
 export const WEBSITE_URL_HELP_TEXT = i18n.translate(
   'xpack.synthetics.monitorManagement.websiteUrlHelpText',
   {