style: replace em dashes in the scaffold comments

cmd/gasm/scaffold.go

@@ -19,7 +19,7 @@ import (
 // file: a Go test that seeds random states, drives both the assembly kernel
 // and a caller-provided portable reference, and compares the outputs
 // byte-for-byte.  The lesson this encodes: a pipeline-level fuzz cannot see
-// an unwired kernel — only a direct-call differential against the portable
+// an unwired kernel, only a direct-call differential against the portable
 // specification can, so every kernel ships with one.
 //
 // The generated file follows two conventions the caller fills in: