Remove old migration code. #2934

Job	Run time
Linux x64 - Build - Profile 'debug'	2m 53s
Linux x64 - Build - Profile 'debug'	2m 53s
Linux x64 - Test	3m 17s
Linux x64 - Test	3m 17s
Linux aarch64 - Build - Profile 'debug'	2m 47s
Linux aarch64 - Build - Profile 'debug'	2m 47s
Linux aarch64 - Test	3m 15s
Linux aarch64 - Test	3m 15s
macOS x64 - Build - Profile 'debug'	3m 46s
macOS x64 - Build - Profile 'debug'	6m 19s
macOS x64 - Test	3m 51s
macOS x64 - Test	7m 9s
macOS aarch64 - Build - Profile 'debug'	3m 28s
macOS aarch64 - Build - Profile 'debug'	3m 28s
macOS aarch64 - Test	3m 42s
macOS aarch64 - Test	5m 25s
Windows x64 - Build - Profile 'debug'	3m 43s
Windows x64 - Build - Profile 'debug'	6m 36s
Windows x64 - Test	3m 45s
Windows x64 - Test	7m 13s
Clippy	3m 25s
Clippy	3m 25s
Rustfmt	2m 42s
Rustfmt	2m 42s
	1h 35m 3s

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