Remove direct dependency on pflag

We weren't actually using pflag, except as an interface assertion.  This
makes it more obvious that pflag isn't actually used.

Author: DirectXMan12

go.mod

@@ -13,7 +13,6 @@ require (
 	github.com/onsi/gomega v1.8.1
 	github.com/prometheus/client_golang v1.0.0
 	github.com/prometheus/client_model v0.0.0-20190129233127-fd36f4220a90
-	github.com/spf13/pflag v1.0.5
 	go.uber.org/zap v1.10.0
 	golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550 // indirect
 	golang.org/x/sys v0.0.0-20190922100055-0a153f010e69 // indirect

pkg/log/zap/flags.go

@@ -23,11 +23,13 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/spf13/pflag"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 )
 
+// each of these flags also should implement the flag.Value, as well
+// as pflag.Value for convinience.
+
 var levelStrings = map[string]zapcore.Level{
 	"debug":  zap.DebugLevel,
 	"-1":     zap.DebugLevel,
@@ -46,8 +48,6 @@ type encoderFlag struct {
 	value   string
 }
 
-var _ pflag.Value = &encoderFlag{}
-
 func (ev *encoderFlag) String() string {
 	return ev.value
 }
@@ -85,8 +85,6 @@ type levelFlag struct {
 	value   string
 }
 
-var _ pflag.Value = &levelFlag{}
-
 func (ev *levelFlag) Set(flagValue string) error {
 	level, validLevel := levelStrings[strings.ToLower(flagValue)]
 	if !validLevel {
@@ -119,8 +117,6 @@ type stackTraceFlag struct {
 	value   string
 }
 
-var _ pflag.Value = &stackTraceFlag{}
-
 func (ev *stackTraceFlag) Set(flagValue string) error {
 	level, validLevel := levelStrings[strings.ToLower(flagValue)]
 	if !validLevel {