Revert Locale behavior of Currency.get{Symbol,DisplayName}

AOSP commit 6d48c53a changed
those methods to use the DISPLAY Locale rather than the
default Locale. We do want the new behavior, but it should
be in a targeted CL with corresponding tests.

Therefore, this CL temporarily reverts these two lines
to the old behavior, followed by another small CL that
reintroduces the new behavior and adds tests.

Bug: 29935305
Bug: 31794800

Test: libcore.java.util.CurrencyTest
Test: org.apache.harmony.tests.java.util.CurrencyTest
Change-Id: Ic84f3e191baa441b8e6d367ce04d8fe7b5ddd6d0