Refine golangci-lint settings (#293)

.github/linters/.golangci.yml

@@ -1,7 +1,5 @@
 run:
   timeout: 5m
-  skip-dirs:
-    - external
   skip-files:
     - generated.*
 
@@ -10,24 +8,16 @@ issues:
   exclude-rules:
     - path: _test\.go
       linters:
-        - gocyclo
         - errcheck
-        - dupl
         - gosec
-        - goconst
 
 linters:
   enable:
     - bodyclose
-    - deadcode
     - depguard
-    - dogsled
-    - dupl
     - errcheck
     - exhaustive
-    - goconst
     - gocritic
-    - gocyclo
     - gofmt
     - goimports
     - golint
@@ -52,3 +42,5 @@ linters:
     - unused
     - varcheck
     - whitespace
+  disable:
+    - deadcode