CLEANUP: tree-wide: remove a few rare non-ASCII chars

As reported by Tim in issue #1428, our sources are clean, there are
just a few files with a few rare non-ASCII chars for the paragraph
symbol, a few typos, or in Fred's name. Given that Fred already uses
the non-accentuated form at other places like on the public list,
let's uniformize all this and make sure the code displays equally
everywhere.
diff --git a/include/import/ist.h b/include/import/ist.h
index 539a27d..978fb3c 100644
--- a/include/import/ist.h
+++ b/include/import/ist.h
@@ -863,7 +863,7 @@
 static inline struct ist istalloc(const size_t size)
 {
 	/* Note: do not use ist2 here, as it triggers a gcc11 warning.
-	 * ‘<unknown>’ may be used uninitialized [-Werror=maybe-uninitialized]
+	 * €˜<unknown>€™ may be used uninitialized [-Werror=maybe-uninitialized]
 	 *
 	 * This warning is reported because the uninitialized memory block
 	 * allocated by malloc should not be passed to a const argument as in