remove useUTC deprecation, set default timezone to local (#22696)

* remove useUTC deprecation, set default timezone to local

* no-unused-vars

* rm set, unset import

docs/migration/migrate_8_0.asciidoc

@@ -18,4 +18,10 @@ The following section is re-used in the Installation and Upgrade Guide
 ////
 // tag::notable-breaking-changes[]
 
+[float]
+=== Default logging timezone is now the system's timezone
+*Details:* In prior releases the timezone used in logs defaulted to UTC.  We now use the host machine's timezone by default.
+
+*Impact:* To restore the previous behavior, in kibana.yml set `logging.timezone: UTC`.
+
 // end::notable-breaking-changes[]

src/legacy/server/config/schema.js

@@ -152,7 +152,7 @@ export default () => Joi.object({
         then: Joi.default(!process.stdout.isTTY),
         otherwise: Joi.default(true)
       }),
-    timezone: Joi.string().allow(false).default('UTC')
+    timezone: Joi.string()
   }).default(),
 
   ops: Joi.object({

src/legacy/server/config/transform_deprecations.js

@@ -17,9 +17,8 @@
  * under the License.
  */
 
-import _, { set } from 'lodash';
+import _ from 'lodash';
 import { createTransform, Deprecations } from '../../deprecation';
-import { unset } from '../../utils';
 
 const { rename, unused } = Deprecations;
 
@@ -46,15 +45,6 @@ const rewriteBasePath = (settings, log) => {
   }
 };
 
-const loggingTimezone = (settings, log) => {
-  if (_.has(settings, 'logging.useUTC')) {
-    const timezone = settings.logging.useUTC ? 'UTC' : false;
-    set('logging.timezone', timezone);
-    unset(settings, 'logging.useUTC');
-    log(`Config key "logging.useUTC" is deprecated. It has been replaced with "logging.timezone"`);
-  }
-};
-
 const deprecations = [
   //server
   unused('server.xsrf.token'),
@@ -66,7 +56,6 @@ const deprecations = [
   rename('optimize.lazyProxyTimeout', 'optimize.watchProxyTimeout'),
   savedObjectsIndexCheckTimeout,
   rewriteBasePath,
-  loggingTimezone,
 ];
 
 export const transformDeprecations = createTransform(deprecations);