Don't use provideWalletChains anymore

[esteblock]

What problem does your feature solve?

Functions and variables defined in wallet/provideWalletChains,tsx are confusing. At the end it does only add a iconBackground parameter to each chain.

What would you like to see?

We could avoid this either:

• not using the iconBackground" parameter,
• setting the iconBackground parameter in the @soroban-react/chains library
• setting localy the iconBackground parameter in a more elegant way

setIconBacground(chain){
if (chain == chain1) return background1
else if (chain == chain2) return backgorund2
.
.
.

[esteblock]

Solved in https://github.com/stellar/soroban-example-dapp/pull/111