Fix linter errors

Mostly comment issues and unused variables.

Signed-off-by: Lukasz Mierzwa <l.mierzwa@gmail.com>

model/labels/labels_stringlabels.go

@@ -76,7 +76,7 @@ func (ls Labels) IsZero() bool {
 
 // MatchLabels returns a subset of Labels that matches/does not match with the provided label names based on the 'on' boolean.
 // If on is set to true, it returns the subset of labels that match with the provided label names and its inverse when 'on' is set to false.
-// TODO: This is only used in printing an error message
+// TODO: This is only used in printing an error message.
 func (ls Labels) MatchLabels(on bool, names ...string) Labels {
 	b := NewBuilder(ls)
 	if on {
@@ -298,6 +298,7 @@ func Equal(ls, o Labels) bool {
 func EmptyLabels() Labels {
 	return Labels{}
 }
+
 func yoloBytes(s string) []byte {
 	return unsafe.Slice(unsafe.StringData(s), len(s))
 }
@@ -370,7 +371,7 @@ func Compare(a, b Labels) int {
 	return +1
 }
 
-// Copy labels from b on top of whatever was in ls previously, reusing memory or expanding if needed.
+// CopyFrom will copy labels from b on top of whatever was in ls previously, reusing memory or expanding if needed.
 func (ls *Labels) CopyFrom(b Labels) {
 	ls.data = b.data // strings are immutable
 }
@@ -440,11 +441,11 @@ func (ls Labels) DropMetricName() Labels {
 }
 
 // InternStrings is a no-op because it would only save when the whole set of labels is identical.
-func (ls *Labels) InternStrings(intern func(string) string) {
+func (ls *Labels) InternStrings(_ func(string) string) {
 }
 
 // ReleaseStrings is a no-op for the same reason as InternStrings.
-func (ls Labels) ReleaseStrings(release func(string)) {
+func (ls Labels) ReleaseStrings(_ func(string)) {
 }
 
 // Builder allows modifying Labels.
@@ -561,7 +562,7 @@ func encodeVarint(data []byte, offset int, v uint64) int {
 	return base
 }
 
-// Special code for the common case that a size is less than 128
+// Special code for the common case that a size is less than 128.
 func encodeSize(data []byte, offset, v int) int {
 	if v < 1<<7 {
 		offset--
@@ -630,7 +631,7 @@ func (b *ScratchBuilder) Add(name, value string) {
 	b.add = append(b.add, Label{Name: name, Value: value})
 }
 
-// Add a name/value pair, using []byte instead of string to reduce memory allocations.
+// UnsafeAddBytes adds a name/value pair using []byte instead of string to reduce memory allocations.
 // The values must remain live until Labels() is called.
 func (b *ScratchBuilder) UnsafeAddBytes(name, value []byte) {
 	b.add = append(b.add, Label{Name: yoloString(name), Value: yoloString(value)})
@@ -658,7 +659,7 @@ func (b *ScratchBuilder) Labels() Labels {
 	return b.output
 }
 
-// Write the newly-built Labels out to ls, reusing an internal buffer.
+// Overwrite will write the newly-built Labels out to ls, reusing an internal buffer.
 // Callers must ensure that there are no other references to ls, or any strings fetched from it.
 func (b *ScratchBuilder) Overwrite(ls *Labels) {
 	size := labelsSize(b.add)
@@ -671,7 +672,7 @@ func (b *ScratchBuilder) Overwrite(ls *Labels) {
 	ls.data = yoloString(b.overwriteBuffer)
 }
 
-// Symbol-table is no-op, just for api parity with dedupelabels.
+// SymbolTable is no-op, just for api parity with dedupelabels.
 type SymbolTable struct{}
 
 func NewSymbolTable() *SymbolTable { return nil }