CI: remove errcheck linter

The errcheck linter causes too many false positives to be useful.
For example, running the upstream errcheck binary flags a ton of
"unchecked" defer Close() calls which are probably filtered out
by golangci-lint.

As an appeal to authority, Cilium proper doesn't have errcheck
enabled either. And the author of the high quality staticcheck
has said that implementing errcheck without a high false positive
rate is not possible.

Just disable the linter.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

.golangci.yaml

@@ -9,7 +9,6 @@ issues:
 linters:
   disable-all: true
   enable:
-    - errcheck
     - goimports
     - gosimple
     - govet
@@ -19,8 +18,3 @@ linters:
     - typecheck
     - unused
     - gofmt
-
-    # Could be enabled later:
-    # - gocyclo
-    # - maligned
-    # - gosec