Remove deprecated `Bundler.clean`, and `Bundler.environment` helpers #1547

Job	Run time
Bundler on read-only system (ruby-3.3)	21s
Bundler on read-only system (ruby-3.2)	21s
Bundler on read-only system (ruby-3.4)	23s
All read-only jobs pass	5s
	1m 10s

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