Remove duplicate dep, x-pack/yarn.lock (#26642)

x-pack/.gitignore

@@ -10,3 +10,6 @@
 /.env
 /.kibana-plugin-helpers.dev.*
 !/plugins/infra/**/target
+
+# We don't want any yarn.lock files in here
+/yarn.lock

x-pack/package.json

@@ -116,13 +116,12 @@
     "yargs": "4.8.1"
   },
   "dependencies": {
-    "@elastic/datemath": "^4.0.2",
+    "@elastic/datemath": "5.0.0",
     "@elastic/eui": "5.3.0",
     "@elastic/node-crypto": "0.1.2",
     "@elastic/node-phantom-simple": "2.2.4",
     "@elastic/numeral": "2.3.2",
     "@kbn/babel-preset": "1.0.0",
-    "@elastic/datemath": "5.0.0",
     "@kbn/es-query": "1.0.0",
     "@kbn/i18n": "1.0.0",
     "@kbn/ui-framework": "1.0.0",