SwapHotkey: No self-loop check for childkeys

[gztensor]

When the swap hotkey is performed, there is no check that new_hotkey is not a child of old_hotkey. This is possible to happen before child keys do not have to be registered on any network when added.

1. Add this check
2. Write a migration that will remove any self-looped ChildKeys or ParentKeys entries

Below are several examples of self-looping on mainnet:

Constraint error: 1 cycle detected (self-loop) at 5F4pBNBg9JYUGk73ahd4vojhEJsoJNgDKNkGD2p7GHcZ6us4 on netuid 4
Constraint error: 1 cycle detected (self-loop) at 5ERJ3ixrtcPBqaib85MeivPNWuiPxE3taKymENb8DvCcbixA on netuid 41
Constraint error: 1 cycle detected (self-loop) at 5DFZEJwgkg98h1kyngSEMYY1NnxXE9tkpLGCtQqf9XCtGBxf on netuid 25
Constraint error: 1 cycle detected (self-loop) at 5GYb7bJqRgHm1oJMG783fAJgsiEwH7Fu3MWGKnCkMmzCqRnh on netuid 13
Constraint error: 1 cycle detected (self-loop) at 5FAC51a9Jc3BoHcpGT28Dg3qNPxPViztTB7fA1MHHdKK3gm1 on netuid 2
Constraint error: 1 cycle detected (self-loop) at 5D4nngxbaX57zkibiP6zjszwx4pyuqoyocQdBCzRvNpw7Z5H on netuid 6
Constraint error: 1 cycle detected (self-loop) at 5GBXyD3nxGkCJ9n8gSSr9hhKDJk7osHNGu5YuVtEMSdY5Ymw on netuid 10
Constraint error: 1 cycle detected (self-loop) at 5DFPWPnmLx7BAqVtzhwAHcFv2AkW5aAPD6uAbFx6DNAHR185 on netuid 11
Constraint error: 1 cycle detected (self-loop) at 5GYfucMhtD4MVy2JqDdeV7v2aA5kd7uZBpqmz8FPFRPK3Ser on netuid 14
Constraint error: 1 cycle detected (self-loop) at 5Fy7fGd2FFdmtyAfuer7SepdtbySPGewF8oVmGNb5A4wHMYM on netuid 23
Constraint error: 1 cycle detected (self-loop) at 5GphK6ZyY3gg1ZBaDfeeNZ4yeyZpc3d7ZpXedN4x9ij2jSGV on netuid 27
Constraint error: 1 cycle detected (self-loop) at 5DiGnqvBzXHnBswkkD7vcU9aA9Spiqq6H6YPXzE575DASUDS on netuid 30
Constraint error: 1 cycle detected (self-loop) at 5FbGp2hED3EftnxVuTF1rihUA9TMyGrRpe77bvYDAXF9VH1F on netuid 33
Constraint error: 1 cycle detected (self-loop) at 5EbmqAcg7LuNUM1H5QcYNjjWCPT51JCfiLURX2py2WZSXWxu on netuid 42
Constraint error: 1 cycle detected (self-loop) at 5HaxWC6iEm66ePS9WX9QRjqEJDQHWS2v1YfoXSgRxnHcKsGb on netuid 50
Constraint error: 1 cycle detected (self-loop) at 5DkUT93xhK6PxFSvWVKSAWjJSXVc9CagdpUm3HwBDPHFCozY on netuid 51
Constraint error: 1 cycle detected (self-loop) at 5G7Cm6SDeCz4YZhoZrfLXFShqTra5bag4GgCCi9eoCN4bp6U on netuid 53
Constraint error: 1 cycle detected (self-loop) at 5GRbxcRk3x7DqTsyi9ucGVsF43hrSLM7CXmiSWjr7UeKCdXc on netuid 64
Constraint error: 1 cycle detected (self-loop) at 5EXXUEhZmqG9fzyURV6YfqEEAHK1gwrKpfVD57iHgq7Wss68 on netuid 68
Constraint error: 1 cycle detected (self-loop) at 5EyXAU6APD5FL3syTsL8JjFt2GtMNTXb72KxQRkwz5Wt3Jwr on netuid 73
Constraint error: 1 cycle detected (self-loop) at 5FcVt2QMozActVwMsLk9EW62o9G6NF8iSfqeZKb7o1WBzQEo on netuid 81
Constraint error: 1 cycle detected (self-loop) at 5C5o2nFjs2o7yPzwZSDn1AWntCbHrv9mF8TmUYrhaT6Ssn91 on netuid 91
Constraint error: 1 cycle detected (self-loop) at 5FUPAUQPGXUqWvAn71qWKMaZjjWGbsEVjVuQoCRekUwvHs93 on netuid 93
Constraint error: 1 cycle detected (self-loop) at 5G6DS5G5UQHUgJCNPHPX5f49VkXbZWd9KpDz4kQ7kjCsn1oo on netuid 100
Constraint error: 1 cycle detected (self-loop) at 5DAjvdMgvyBGQ1WHWchdu2gJv8yYVwUy8guY67Ytcp6Rs1o2 on netuid 102
Constraint error: 1 cycle detected (self-loop) at 5CJQ7NPaVifP2dops1f9Y9peWT124sbyg4eH6AKzsjJqmKis on netuid 44
Constraint error: 1 cycle detected (self-loop) at 5HWAkovqTiGXbo4VeMYLACThDPuzFgWrg27SaXmqXGGpGGPh on netuid 63