Revert "Build Ruby 3.0 for old distributions"

[k0kubun]

Reverts #27

🤔

https://github.com/ruby/ruby/actions/runs/7924405332/job/21635896944?pr=9986

Extracting bundle gem minitest-5.22.2...
Extracting bundle gem power_assert-2.0.3...
Extracting bundle gem rake-13.1.0...
../src/revision.h unchanged
Extracting bundle gem test-unit-3.6.1...
<internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require': /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so: undefined symbol: inflateReset - /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so (LoadError)
	from <internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:195:in `initialize'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /__w/ruby/ruby/src/tool/lib/bundled_gem.rb:[12](https://github.com/ruby/ruby/actions/runs/7924405332/job/21635896944?pr=9986#step:10:13):in `unpack'
	from -e:1:in `<main>'
<internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require': /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so: undefined symbol: inflateReset - /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so (LoadError)
	from <internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:195:in `initialize'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /__w/ruby/ruby/src/tool/lib/bundled_gem.rb:12:in `unpack'
	from -e:1:in `<main>'
make: *** [../src/defs/gmake.mk:357: ../src/.bundle/gems/rake-[13](https://github.com/ruby/ruby/actions/runs/7924405332/job/21635896944?pr=9986#step:10:14).1.0] Error 1
make: *** Waiting for unfinished jobs....
<internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require': /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so: undefined symbol: inflateReset - /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so (LoadError)
	from <internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:195:in `initialize'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:[16](https://github.com/ruby/ruby/actions/runs/7924405332/job/21635896944?pr=9986#step:10:17)0:in `new'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /__w/ruby/ruby/src/tool/lib/bundled_gem.rb:12:in `unpack'
	from -e:1:in `<main>'
make: *** [../src/defs/gmake.mk:357: ../src/.bundle/gems/power_assert-2.0.3] Error 1
make: *** [../src/defs/gmake.mk:357: ../src/.bundle/gems/minitest-5.22.2] Error 1
<internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require': /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so: undefined symbol: inflateReset - /usr/local/lib/ruby/3.0.0/x86_64-linux/zlib.so (LoadError)
	from <internal:/usr/local/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:195:in `initialize'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /usr/local/lib/ruby/3.0.0/rubygems/package.rb:160:in `new'
	from /__w/ruby/ruby/src/tool/lib/bundled_gem.rb:12:in `unpack'
	from -e:1:in `<main>'
make: *** [../src/defs/gmake.mk:[35](https://github.com/ruby/ruby/actions/runs/7924405332/job/21635896944?pr=9986#step:10:36)7: ../src/.bundle/gems/test-unit-3.6.1] Error 1