8017325, 8017326: Cleanup of javadoc <code> tag

[Jason Uh]

Joe, all,

Could I please get a review of the following changes?

These changesets convert the <code>...</code> javadoc tags to {@code 
...} as part of an overall effort to clean up doclint warnings.

Webrevs --
- java.security.cert:
     http://cr.openjdk.java.net/~juh/8017325/webrev.00/
- java.security.spec:
     http://cr.openjdk.java.net/~juh/8017326/webrev.00/

specdiff reported no changes in the generated docs.

More of these to come.

Thanks,
Jason