tree-wide: add spdx header on source files

version.h is tiny, but the other two certainly deserve a license header.

src/journal-remote/browse.html

@@ -1,4 +1,5 @@
 <!DOCTYPE html>
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
 <html>
 <head>
         <title>Journal</title>

src/shared/openssl-util.c

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
 #include "openssl-util.h"
 #include "alloc-util.h"
 

src/version/version.h.in

@@ -1,4 +1,6 @@
-/* Detailed project version that includes git commit when not built from a release.
+/* SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * Detailed project version that includes git commit when not built from a release.
  * Use this in preference to PROJECT_VERSION, with the following exceptions:
  * - where a simplified form is expected for compatibility, for example
  *   'udevadm version',