[11u] RFR (XS) 8253220: Epsilon: clean up unused code/declarations

[Aleksey Shipilev]

Original RFE:
    https://bugs.openjdk.java.net/browse/JDK-8253220
    https://git.openjdk.java.net/jdk/commit/7f9b5d9e

One of the hunks does not apply to 11u, because JDK-8224815 in 14 changed the 
Universe::reserve_heap. 11u still needs reserved region. The other hunk applies and makes the whole 
thing trivial. Still, I would like to backport it to match the code as close as possible.

11u variant:

diff -r 9541a274fe2f src/hotspot/share/gc/epsilon/epsilonBarrierSet.cpp
--- a/src/hotspot/share/gc/epsilon/epsilonBarrierSet.cpp	Sat May 30 20:10:18 2020 -0400
+++ b/src/hotspot/share/gc/epsilon/epsilonBarrierSet.cpp	Fri Jan 08 11:18:12 2021 +0100
@@ -41,7 +41,7 @@
            make_barrier_set_assembler<BarrierSetAssembler>(),
            make_barrier_set_c1<BarrierSetC1>(),
            make_barrier_set_c2<BarrierSetC2>(),
-          BarrierSet::FakeRtti(BarrierSet::EpsilonBarrierSet)) {};
+          BarrierSet::FakeRtti(BarrierSet::EpsilonBarrierSet)) {}

  void EpsilonBarrierSet::on_thread_create(Thread *thread) {
    EpsilonThreadLocalData::create(thread);

Testing: gc/epsilon {fastdebug,release} x {x86_64,aarch64}

-- 
Thanks,
-Aleksey