Fix the golangci-lint config (vitessio#11812)

There's a bunch of deprecated linters that don't work anymore, so let's
remove them:

```
WARN [runner] The linter 'deadcode' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused.
WARN [runner] The linter 'structcheck' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused.
WARN [runner] The linter 'varcheck' is deprecated (since v1.49.0) due to: The owner seems to have abandoned the linter.  Replaced by unused.
WARN [linters context] structcheck is disabled because of generics. You can track the evolution of the generics support by following the golangci/golangci-lint#2649.
```

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>

.golangci.yml

@@ -42,10 +42,6 @@ issues:
       - errcheck
       - goimports
 
-    - path: '^go/vt/vtadmin/cache/'
-      linters:
-      - structcheck
-
     ### BEGIN: errcheck exclusion rules. Each rule should be considered
     #   a TODO for removal after adding error checks to that package/file/etc,
     #   except where otherwise noted.