Remove convert old states code

CHANGELOG.asciidoc

@@ -21,6 +21,7 @@ https://github.com/elastic/beats/compare/v5.1.1...master[Check the HEAD diff]
 
 *Filebeat*
 - Always use absolute path for event and registry. This can lead to issues when relative paths were used before. {pull}3328[3328]
+- Remove code to convert states from 1.x. {pull}3767[3767]
 
 *Heartbeat*
 

filebeat/registrar/registrar.go

@@ -7,8 +7,6 @@ import (
 	"path/filepath"
 	"sync"
 
-	"time"
-
 	cfg "github.com/elastic/beats/filebeat/config"
 	"github.com/elastic/beats/filebeat/input"
 	"github.com/elastic/beats/filebeat/input/file"
@@ -105,12 +103,6 @@ func (r *Registrar) loadStates() error {
 
 	logp.Info("Loading registrar data from %s", r.registryFile)
 
-	// DEPRECATED: This should be removed in 6.0
-	oldStates := r.loadAndConvertOldState(f)
-	if oldStates {
-		return nil
-	}
-
 	decoder := json.NewDecoder(f)
 	states := []file.State{}
 	err = decoder.Decode(&states)
@@ -125,60 +117,6 @@ func (r *Registrar) loadStates() error {
 	return nil
 }
 
-// loadAndConvertOldState loads the old state file and converts it to the new state
-// This is designed so it can be easily removed in later versions
-func (r *Registrar) loadAndConvertOldState(f *os.File) bool {
-	// Make sure file reader is reset afterwards
-	defer f.Seek(0, 0)
-
-	stat, err := f.Stat()
-	if err != nil {
-		logp.Err("Error getting stat for old state: %+v", err)
-		return false
-	}
-
-	// Empty state does not have to be transformed ({} + newline)
-	if stat.Size() <= 4 {
-		return false
-	}
-
-	// Check if already new state format
-	decoder := json.NewDecoder(f)
-	newState := []file.State{}
-	err = decoder.Decode(&newState)
-	// No error means registry is already in new format
-	if err == nil {
-		return false
-	}
-
-	// Reset file offset
-	f.Seek(0, 0)
-	oldStates := map[string]file.State{}
-	err = decoder.Decode(&oldStates)
-	if err != nil {
-		logp.Err("Error decoding old state: %+v", err)
-		return false
-	}
-
-	// No old states found -> probably already new format
-	if oldStates == nil {
-		return false
-	}
-
-	// Convert old states to new states
-	logp.Info("Old registry states found: %v", len(oldStates))
-	states := convertOldStates(oldStates)
-	states = resetStates(states)
-	r.states.SetStates(states)
-
-	// Rewrite registry in new format
-	r.writeRegistry()
-
-	logp.Info("Old states converted to new states and written to registrar: %v", len(oldStates))
-
-	return true
-}
-
 // resetStates sets all states to finished and disable TTL on restart
 // For all states covered by a prospector, TTL will be overwritten with the prospector value
 func resetStates(states []file.State) []file.State {
@@ -192,32 +130,6 @@ func resetStates(states []file.State) []file.State {
 	return states
 }
 
-func convertOldStates(oldStates map[string]file.State) []file.State {
-	// Convert old states to new states
-	states := []file.State{}
-	for _, state := range oldStates {
-		// Makes timestamp time of migration, as this is the best guess
-		state.Timestamp = time.Now()
-
-		// Check for duplicates
-		dupe := false
-		for i, other := range states {
-			if state.FileStateOS.IsSame(other.FileStateOS) {
-				dupe = true
-				if state.Offset > other.Offset {
-					// replace other
-					states[i] = state
-					break
-				}
-			}
-		}
-		if !dupe {
-			states = append(states, state)
-		}
-	}
-	return states
-}
-
 func (r *Registrar) Start() error {
 
 	// Load the previous log file locations now, for use in prospector