libstdc++: Fix tests for uninitialized_value_construct_n

libstdc++: Fix tests for uninitialized_value_construct_n

In my recent r11-1460 commit the tests had been "improved" before
commit, and no longer exercised the code paths changed by the patch.

This restores what I originally tested, so that the tests fail before
the r11-1460 change and pass after it.

	* testsuite/20_util/specialized_algorithms/uninitialized_default_n/sizes.cc:
	Replace Value type with int so trivial code path is used.
	* testsuite/20_util/specialized_algorithms/uninitialized_value_construct_n/sizes.cc:
	Likewise.