Get rid of partitioner locks

they are no longer necessary

partitioner.go

@@ -4,7 +4,6 @@ import (
 	"hash"
 	"hash/fnv"
 	"math/rand"
-	"sync"
 	"time"
 )
 
@@ -18,7 +17,6 @@ type Partitioner interface {
 // RandomPartitioner implements the Partitioner interface by choosing a random partition each time.
 type RandomPartitioner struct {
 	generator *rand.Rand
-	m         sync.Mutex
 }
 
 func NewRandomPartitioner() Partitioner {
@@ -28,15 +26,12 @@ func NewRandomPartitioner() Partitioner {
 }
 
 func (p *RandomPartitioner) Partition(key Encoder, numPartitions int32) int32 {
-	p.m.Lock()
-	defer p.m.Unlock()
 	return int32(p.generator.Intn(int(numPartitions)))
 }
 
 // RoundRobinPartitioner implements the Partitioner interface by walking through the available partitions one at a time.
 type RoundRobinPartitioner struct {
 	partition int32
-	m         sync.Mutex
 }
 
 func NewRoundRobinPartitioner() Partitioner {
@@ -44,8 +39,6 @@ func NewRoundRobinPartitioner() Partitioner {
 }
 
 func (p *RoundRobinPartitioner) Partition(key Encoder, numPartitions int32) int32 {
-	p.m.Lock()
-	defer p.m.Unlock()
 	if p.partition >= numPartitions {
 		p.partition = 0
 	}
@@ -60,7 +53,6 @@ func (p *RoundRobinPartitioner) Partition(key Encoder, numPartitions int32) int3
 type HashPartitioner struct {
 	random Partitioner
 	hasher hash.Hash32
-	m      sync.Mutex
 }
 
 func NewHashPartitioner() Partitioner {
@@ -71,8 +63,6 @@ func NewHashPartitioner() Partitioner {
 }
 
 func (p *HashPartitioner) Partition(key Encoder, numPartitions int32) int32 {
-	p.m.Lock()
-	defer p.m.Unlock()
 	if key == nil {
 		return p.random.Partition(key, numPartitions)
 	}