Fix URLConnectionTest for devices without full internet access.

This removes two bad tests that are covered elsewhere, using
mocks.

test_getContentEncoding() was hitting http://www.amazon.com, to see
if a URLConnection getter was working. That getter is now tested in
libcore/luni/src/test/java/libcore/java/net/URLConnectionTest.java,
in testClientConfiguredGzipContentEncoding().

test_getLastModified() was hitting
http://www.php.net/manual/en/function.explode.php, to see if
getHeaderFieldDate was working for Last-Modified. That getter is
better tested in test_getHeaderFieldDateLjava_lang_StringJ(), in the
same file.

Bug:18480776

(cherry picked from commit 939e6a1aceff448445928ad5d815479e84e84383)

Change-Id: Ia01fd59809683317271017364179e1843c149e65
3 files changed