Remove unused variables/types/functions

[staticcheck](https://staticcheck.io/) reported a number of unused
fields, functions, types, and variables across the code.

Where possible, use them (assert unchecked errors in tests, for example)
and otherwise remove them.

1 files changed, 1 insertions, 0 deletions

diff --git a/config/config_test.go b/config/config_test.go
index 6f0242d..5a51bb3 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -361,6 +361,7 @@ func (s *ConfigSuite) TestRemoveUrlOptions(c *C) {
 	cfg.Remotes["alt"].URLs = []string{}
 
 	buf, err = cfg.Marshal()
+	c.Assert(err, IsNil)
 	if strings.Contains(string(buf), "url") {
 		c.Fatal("conifg should not contain any url sections")
 	}