RFR [9] 8133188: docs: replace <tt> tags (obsolete in html5) for java.util

[Alexander Stepanov]

Hello,

Could you please review the following fix:
http://cr.openjdk.java.net/~avstepan/8133188/webrev.01
for
https://bugs.openjdk.java.net/browse/JDK-8133188

Just a next portion of "<tt>" tags removed.

specdiff report:
http://cr.openjdk.java.net/~avstepan/8133188/specdiff.util/overview-summary.html
  - some constructs like
"<tt>(o==null ? e==null : o.equals(e))</tt>"
were replaced with "{@code Objects.equals(o, e)}"
(e.g., 
http://cr.openjdk.java.net/~avstepan/8133188/webrev.01/src/java.base/share/classes/java/util/LinkedList.java.udiff.html); 
- please see JDK-8133188 comments.

Thanks,
Alexander