Add migration to remove `seedWords` state (#6937)

The `seedWords` state was removed from the PreferencesController
recently in #6920. That state hadn't been used in some time, and there
was a long period during which `seedWords` was periodically scrubbed
from the state, so it's highly unlikely that it still exists in state
for most users. It's hard to guarantee that it _doesn't_ though,
especially if a user hasn't opened MetaMask in a few months.

1 files changed, 28 insertions, 0 deletions

diff --git a/app/scripts/migrations/035.js b/app/scripts/migrations/035.js
new file mode 100644
index 000000000..02b01f588
--- /dev/null
+++ b/app/scripts/migrations/035.js
@@ -0,0 +1,28 @@
+// next version number
+const version = 35
+
+/*
+
+Removes the deprecated 'seedWords' state
+
+*/
+
+const clone = require('clone')
+
+module.exports = {
+  version,
+
+  migrate: async function (originalVersionedData) {
+    const versionedData = clone(originalVersionedData)
+    versionedData.meta.version = version
+    versionedData.data = transformState(versionedData.data)
+    return versionedData
+  },
+}
+
+function transformState (state) {
+  if (state.PreferencesController && state.PreferencesController.seedWords !== undefined) {
+    delete state.PreferencesController.seedWords
+  }
+  return state
+}