clean-up "nolint" comments, remove unused ones

- fix "nolint" comments to be in the correct format (`//nolint:<linters>[,<linter>`
  no leading space, required colon (`:`) and linters.
- remove "nolint" comments for errcheck, which is disabled in our config.
- remove "nolint" comments that were no longer needed (nolintlint).
- where known, add a comment describing why a "nolint" was applied.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

contrib/fuzz/content_fuzzer.go

@@ -14,7 +14,7 @@
    limitations under the License.
 */
 
-// nolint: golint
+//nolint:golint
 package fuzz
 
 import (