community/go: upgrade to 1.18

Removed patches should no longer be needed:

* disable-flaky-gc-test.patch: marked upstream as flaky
  https://github.com/golang/go/commit/d8ceb133cac65b47c3f5bb292fbb28690c8b89a5
* disable-flaky-sync-test.patch: has been "deflaked" upstream
  https://github.com/golang/go/commit/b7f3c178a337b41c78a38dc3223304d69ec592f7