Clean various constructs

Clean various constructs

* Remove intern() on constant strings.
* Avoid some casts by changing test instance types.
* Remove a number of unnecessary type specifiers and casts.
* Remove an unnecessary return.
* Use StringBuilder::append()'s substring parameters instead of a
  separate String::substring().

Change-Id: Iaaa206d233fbc43ed1bed2d651c549643e6e7697
Signed-off-by: Stephen Kitt <skitt@redhat.com>