Plugins: Remove option shows for unremovable plugins

[carinapilar]

Expected behavior

To show the removal option only for plugins that can be removed from a site.

Actual behavior

When you access an Atomic site that has plugins that can't be removed, the app lets you click on the Remove link, but it shows an error when you try to remove it.

Steps to reproduce the behavior

Add an Atomic site on the app and check plugins such as Jetpack, AMP, Gutenberg, etc.

Tested on iPhone Xs, iOS 12.3.1, WPiOS 12.8.2

[designsimply]

Tested and confirmed with WPiOS 13.2.1.2 (TestFlight) on iPhone 6S iOS 13.1 that I see "Error removing AMP" after attempting to remove Atomic-required plugins. (15s)

2019-09-18 18:07:35:796 🔵 Tracked: plugin_directory_opened <blog_id: 105644731>
2019-09-18 18:07:39:055 🔵 Tracked: plugin_list_opened <blog_id: 105644731, type: installed>
2019-09-18 18:07:39:759 TracksService sendQueuedEvents completed. Sent 2 events.
2019-09-18 18:07:52:635 🔵 Tracked: plugin_removed <blog_id: 105644731>
2019-09-18 18:07:53:988 [PluginServiceRemoteError] Error removing plugin: Error Domain=WordPressKit.WordPressComRestApiError Code=7 "Could not fully remove the plugin amp/amp.php." UserInfo={WordPressComRestApiErrorMessageKey=Could not fully remove the plugin amp/amp.php., WordPressComRestApiErrorCodeKey=delete_plugin_error, NSLocalizedDescription=Could not fully remove the plugin amp/amp.php.}
2019-09-18 18:07:53:988 Error removing AMP.
2019-09-18 18:07:53:989 Could not fully remove the plugin amp/amp.php.
2019-09-18 18:07:54:857 TracksService sendQueuedEvents completed. Sent 1 events.