[NFC] Remove unused code in type fuzzer (#5023)
[NFC] Remove unused code in type fuzzer (#5023)

The only call to `generateSubBasic` was removed as part of a bug fix in #4346,
but the function itself was not removed. Remove it and other unused functions it
depends on now.
WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen