chore(linter): remove deprecated linters (#3046)

### Pull Request Checklist

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* [x] I have justified why this PR doesn't need tests - linter setup
changes aren't something testable
* [x] Pull request includes a [sign off below using a legally
identifiable
name](https://matrix-org.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

Signed-off-by: `Marcelina Hołub <mholub@tutanota.com>`

Signed-off-by: Marcelina Hołub <mholub@tutanota.com>
Co-authored-by: kegsay <kegan@matrix.org>

.golangci.yml

@@ -179,7 +179,6 @@ linters-settings:
 
 linters:
   enable:
-    - deadcode
     - errcheck
     - goconst
     - gocyclo
@@ -191,10 +190,8 @@ linters:
     - misspell # Check code comments, whereas misspell in CI checks *.md files
     - nakedret
     - staticcheck
-    - structcheck
     - unparam
     - unused
-    - varcheck
   enable-all: false
   disable:
     - bodyclose