Remove unused `ostruct` #116

Job	Run time
Ruby 2.4 - macos-latest	6s
Ruby 2.5 - macos-latest	6s
Ruby 2.6 - macos-latest	35s
Ruby 2.7 - macos-latest	37s
Ruby 3.0 - macos-latest	26s
Ruby 3.1 - macos-latest	24s
Ruby 3.2 - macos-latest	20s
Ruby 3.3 - macos-latest	24s
Ruby head - macos-latest	18s
Ruby jruby - macos-latest	47s
Ruby jruby-head - macos-latest	37s
Ruby truffleruby - macos-latest	57s
Ruby 2.4 - ubuntu-20.04	25s
Ruby 2.5 - ubuntu-20.04	27s
Ruby 2.6 - ubuntu-20.04	28s
Ruby 2.7 - ubuntu-20.04	28s
Ruby 3.0 - ubuntu-20.04	18s
Ruby 3.1 - ubuntu-20.04	21s
Ruby 3.2 - ubuntu-20.04	21s
Ruby 3.3 - ubuntu-20.04	25s
Ruby head - ubuntu-20.04	15s
Ruby jruby - ubuntu-20.04	55s
Ruby jruby-head - ubuntu-20.04	51s
Ruby truffleruby - ubuntu-20.04	55s
Ruby mingw - windows-latest	1m 40s
Ruby mswin - windows-latest	1m 57s
Ruby jruby - windows-latest	3m 38s
Ruby head - ubuntu-22.04	14s
Ruby 3.1 - ubuntu-22.04	19s
Ruby 3.2 - ubuntu-22.04	17s
Ruby 3.3 - ubuntu-22.04	32s
	20m 23s

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