chore: last token should be stored only per URL

After a successful connection to a deployment URL we used
to save the same token associated with two keys:
- last-token
- and associated with the last url

But it does not make sense, once we have to URL we can easily resolve the token
associated with the URL. In other words this commit removes the ability to read/save
a token associated with `last-token` key.

Author: fioan89

src/main/kotlin/com/coder/toolbox/CoderRemoteProvider.kt

@@ -406,7 +406,6 @@ class CoderRemoteProvider(
         // Store the URL and token for use next time.
         context.settingsStore.updateLastUsedUrl(client.url)
         if (context.settingsStore.requireTokenAuth) {
-            context.secrets.lastToken = client.token ?: ""
             context.secrets.storeTokenFor(client.url, client.token ?: "")
             context.logger.info("Deployment URL and token were stored and will be available for automatic connection")
         } else {

src/main/kotlin/com/coder/toolbox/store/CoderSecretsStore.kt

@@ -8,21 +8,7 @@ import java.net.URL
  * Provides Coder secrets backed by the secrets store service.
  */
 class CoderSecretsStore(private val store: PluginSecretStore) {
-    private fun get(key: String): String = store[key] ?: ""
-
-    private fun set(key: String, value: String) {
-        if (value.isBlank()) {
-            store.clear(key)
-        } else {
-            store[key] = value
-        }
-    }
-
-    val lastDeploymentURL: String
-        get() = get("last-deployment-url")
-    var lastToken: String
-        get() = get("last-token")
-        set(value) = set("last-token", value)
+    val lastDeploymentURL: String = store["last-deployment-url"] ?: ""
 
     fun tokenFor(url: URL): String? = store[url.host]