fix: update example contract

[matklad]

No description provided.

[matklad]

Ideally, I would like to add an integration test to near-vm-runner-standalone which runs cargo build example-contract, to make sure this doesn't regress in the future. I am not sure that would be a good idea. I have a couple of questions regarding to that:

• can we stomach CI time increase by CPU minute? Compiling even the empty contract takes a lot of time, as it uses full syn, and near_sdk is pretty heavy.
• what is the compatibility story between near-sdk and nearcore? The contract has to depend on a published version of nearsdk. Can it be the case that the published version of nearsdk becomes incompatible with the master of nearcore?

[willemneal]

I think it would be a good idea to not depend an the sdk to compile the contract. @evgenykuzyakov had a recent example, but I can't find it.

[matklad]

Yeah, actually, I've found a bunch of better maintained contracts in this repository. I think we can remove this example instead of upgrading it to the modern sdk version?