Remove sparc64 trademark

We don't reference sparc64 in either of these chapters, so remove it from the
trademark list.

documentation/content/en/articles/committers-guide/_index.adoc

@@ -4,7 +4,7 @@ authors:
   - author: The FreeBSD Documentation Project
 copyright: 1999-2019 The FreeBSD Documentation Project
 releaseinfo: "$FreeBSD$" 
-trademarks: ["freebsd", "coverity", "ibm", "intel", "sparc", "general"]
+trademarks: ["freebsd", "coverity", "ibm", "intel", "general"]
 ---
 
 = Committer's Guide

documentation/content/en/articles/explaining-bsd/_index.adoc

@@ -4,7 +4,7 @@ authors:
   - author: Greg Lehey
     email: grog@FreeBSD.org
 releaseinfo: "$FreeBSD$" 
-trademarks: ["freebsd", "amd", "apple", "intel", "linux", "opengroup", "sparc", "sun", "unix", "general"]
+trademarks: ["freebsd", "amd", "apple", "intel", "linux", "opengroup", "sun", "unix", "general"]
 ---
 
 = Explaining BSD