Remove TimeZoneTest.testAllDisplayNames

Remove testAllDisplayNames from libcore.java.util.TimeZoneTest, because
it is a very slow test with a very low signal quality.

It iterates over all available locales (a growing set) and all available
Timezones (ditto) and just verifies that a non-null display name is
returned. It also never seems to have failed at any point, outside of
timeouts.

Instead add a hand-selected (basically arbitrary) number of locales to
which to apply the testDisplayName() checks (previously just done on
en-US).

Bug: 22786792
Test: vogar luni/src/test/java/libcore/java/util/TimeZoneTest.java
Change-Id: Icc96570955b4f9e95e1854398de121a094b17453