*: reflow comments to 80 characters

This reformats the entire Metropolis codebase to have comments no longer
than 80 characters, implementing CR/66.

This has been done half manually, as we don't have a good integration
between commentwrap/Bazel, but that can be implemented if we decide to
go for this tool/limit.

Change-Id: If1fff0b093ef806f5dc00551c11506e8290379d0
diff --git a/metropolis/pkg/erofs/compression.go b/metropolis/pkg/erofs/compression.go
index 58b2f4b..dca9946 100644
--- a/metropolis/pkg/erofs/compression.go
+++ b/metropolis/pkg/erofs/compression.go
@@ -21,8 +21,8 @@
 
 import "encoding/binary"
 
-// mapHeader is a legacy but still-used advisory structure at the start of a compressed VLE block. It contains constant
-// values as annotated.
+// mapHeader is a legacy but still-used advisory structure at the start of a
+// compressed VLE block. It contains constant values as annotated.
 type mapHeader struct {
 	Reserved      uint32 // 0
 	Advise        uint16 // 1