Revert "soroban-rpc: update go package dependencies"

[2opremio]

Reverts #1030

It enforces using Go 1.21 to compile soroban-tools

[2opremio]

For some reason go mod tidy tries to install [email protected] even if I downgrade jrpc2 to jrpc2 to v1.1.0

% go mod tidy -go=1.20   
go: finding module for package github.com/google/shlex
go: found github.com/google/shlex in github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
go: github.com/creachadair/[email protected] requires [email protected], but 1.20 is requested

[willemneal]

Why not upgrade to the 1.21?

[2opremio]

Because we want to support the last 2 go releases (at least in stellar/go)

[2opremio]

OK, it seems the problem is stellar/go is also broken :(

alfonsoacosta@macbookM2Max soroban-tools % go mod graph | grep mds
github.com/stellar/soroban-tools github.com/creachadair/[email protected]
github.com/creachadair/[email protected] github.com/creachadair/[email protected]
github.com/creachadair/[email protected] github.com/google/[email protected]
github.com/creachadair/[email protected] [email protected]
github.com/stellar/[email protected] github.com/creachadair/[email protected]

[2opremio]

See stellar/go#5088 . We should do the same in soroban-rpc next