Remove last lingering unnecessarily exported functions

fixes #3262

There are a few things left, either by design or uncertainty:
* `pkg/apis/pipeline/v1beta1/conversion_error.go`'s `ConvertErrorf` - I'm not entirely clear on whether this should be around or not. `CannotConvertError` is still used in tests in `pkg/apis/pipeline/v1alpha1`, and the whole thing is just messy enough that I'm not sure what to do.
* `pkg/apis/pipeline/v1beta1/version_validation.go`'s `ValidateEnabledAPIFields` - it's referenced in `docs/developers/README.md` and I can't tell if that's something that could be intended to eb used in something depending on Tekton, not just in Tekton itself.
* `pkg/pipelinerunmetrics/injection.go` and `pkg/taskrunmetrics/injection.go`'s `WithInformer` - these are both used as function references in their respective `.../fake/fake.go`s.

Signed-off-by: Andrew Bayer <andrew.bayer@gmail.com>

pkg/apis/config/metrics.go

@@ -117,8 +117,8 @@ func (cfg *Metrics) Equals(other *Metrics) bool {
 		other.DurationPipelinerunType == cfg.DurationPipelinerunType
 }
 
-// NewMetricsFromMap returns a Config given a map corresponding to a ConfigMap
-func NewMetricsFromMap(cfgMap map[string]string) (*Metrics, error) {
+// newMetricsFromMap returns a Config given a map corresponding to a ConfigMap
+func newMetricsFromMap(cfgMap map[string]string) (*Metrics, error) {
 	tc := Metrics{
 		TaskrunLevel:            DefaultTaskrunLevel,
 		PipelinerunLevel:        DefaultPipelinerunLevel,
@@ -144,5 +144,5 @@ func NewMetricsFromMap(cfgMap map[string]string) (*Metrics, error) {
 
 // NewArtifactBucketFromConfigMap returns a Config for the given configmap
 func NewMetricsFromConfigMap(config *corev1.ConfigMap) (*Metrics, error) {
-	return NewMetricsFromMap(config.Data)
+	return newMetricsFromMap(config.Data)
 }

pkg/apis/config/store.go

@@ -53,7 +53,7 @@ func FromContextOrDefaults(ctx context.Context) *Config {
 	featureFlags, _ := NewFeatureFlagsFromMap(map[string]string{})
 	artifactBucket, _ := NewArtifactBucketFromMap(map[string]string{})
 	artifactPVC, _ := NewArtifactPVCFromMap(map[string]string{})
-	metrics, _ := NewMetricsFromMap(map[string]string{})
+	metrics, _ := newMetricsFromMap(map[string]string{})
 	return &Config{
 		Defaults:       defaults,
 		FeatureFlags:   featureFlags,
@@ -121,7 +121,7 @@ func (s *Store) Load() *Config {
 
 	metrics := s.UntypedLoad(GetMetricsConfigName())
 	if metrics == nil {
-		metrics, _ = NewMetricsFromMap(map[string]string{})
+		metrics, _ = newMetricsFromMap(map[string]string{})
 	}
 	return &Config{
 		Defaults:       defaults.(*Defaults).DeepCopy(),