[chore] Remove deprecated linters

Linters varcheck and deadcode were deprecated since v1.49.0 because the owners
have abandoned them. Both are replaced with unused, see details here
golangci/golangci-lint#1841

Author: Valentin Rodygin

.golangci.yml

@@ -12,7 +12,6 @@ run:
 linters:
   disable-all: true
   enable:
-    - deadcode
     - goconst
     - goimports
     - gosimple
@@ -21,8 +20,7 @@ linters:
     - misspell
     # - staticcheck
     - unconvert
-    # - unused
-    - varcheck
+    - unused
 
     # - gosec
     # - errcheck