remove empty gentx

[liamsi]

Removes the empty file in gentxs. CI currently fails b/c of that: e.g. see: https://github.com/celestiaorg/networks/actions/runs/6597322353/job/17924241218?pr=362

Run if test -f ./celestia/pre-genesis.json; then
Error: EOF: tx parse error
Usage: [...]

[MSevey]

github will also remove empty directories, so run-network will continue to fail until the first gentx is added.

i think the fix here is to add a readme.md file to the gentx directory. the markdown file shouldn't be read by the genutil tool so it shouldn't impact the CI.

[liamsi]

github will also remove empty directories, so run-network will continue to fail until the first gentx is added.

But in PRs people create a gentx directory. So CI won't fail for each PR, right? also the gentest tool will fail on a readme.md as well.

[liamsi]

closing in favour of #367