internal/fuzz: fix names of noCopy methods

Must be Lock/Unlock to be flagged by vet.

Change-Id: I792ebd68b168621a660b9595b5d06a465d0d7bf2
Reviewed-on: https://go-review.googlesource.com/c/go/+/584355
Auto-Submit: Roland Shoemaker <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: alexandear

src/internal/fuzz/pcg.go

@@ -140,6 +140,6 @@ func (r *pcgRand) bool() bool {
 // for details.
 type noCopy struct{}
 
-// lock is a no-op used by -copylocks checker from `go vet`.
-func (*noCopy) lock()   {}
-func (*noCopy) unlock() {}
+// Lock is a no-op used by -copylocks checker from `go vet`.
+func (*noCopy) Lock()   {}
+func (*noCopy) Unlock() {}