Delete link replies if no embed generated

[ericthelemur]

Currently apollo blindly replies to e.g. instagram links, but sometimes they are search or account links with no embed, so it's a wasted message.

Either

• Improve the detection to avoid these cases
• or delete the embed if no embed is actually generated by the 2nd one (or the original message has a better embed)

[raven0034]

I imagine a fair bit of this can be dealt with using regex then use the second point as a fallback.

Also e.g. in the case of Twitter links, the Twitter embed, even when it is sometimes working, is worse than the fxtwitter alternative e.g. when there is a video attached to the tweet. ie worth considering on a platform by platform basis.