libstdc++: Remove redundancy in test pathnames

Repeating "explicit_instantiation" in these long pathnames is not
necessary.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/duration/requirements/explicit_instantiation/explicit_instantiation.cc:
	Moved to...
	* testsuite/20_util/duration/requirements/explicit_instantiation.cc: ...here.
	* testsuite/20_util/time_point/requirements/explicit_instantiation/explicit_instantiation.cc:
	Moved to...
	* testsuite/20_util/time_point/requirements/explicit_instantiation.cc: ...here.
	* testsuite/20_util/unique_ptr/requirements/explicit_instantiation/explicit_instantiation.cc:
	Moved to...
	* testsuite/20_util/unique_ptr/requirements/explicit_instantiation.cc: ...here.

diff --git a/libstdc++-v3/testsuite/20_util/duration/requirements/explicit_instantiation/explicit_instantiation.cc b/libstdc++-v3/testsuite/20_util/duration/requirements/explicit_instantiation.cc
similarity index 100%
rename from libstdc++-v3/testsuite/20_util/duration/requirements/explicit_instantiation/explicit_instantiation.cc
rename to libstdc++-v3/testsuite/20_util/duration/requirements/explicit_instantiation.cc

diff --git a/libstdc++-v3/testsuite/20_util/time_point/requirements/explicit_instantiation/explicit_instantiation.cc b/libstdc++-v3/testsuite/20_util/time_point/requirements/explicit_instantiation.cc
similarity index 100%
rename from libstdc++-v3/testsuite/20_util/time_point/requirements/explicit_instantiation/explicit_instantiation.cc
rename to libstdc++-v3/testsuite/20_util/time_point/requirements/explicit_instantiation.cc

diff --git a/libstdc++-v3/testsuite/20_util/unique_ptr/requirements/explicit_instantiation/explicit_instantiation.cc b/libstdc++-v3/testsuite/20_util/unique_ptr/requirements/explicit_instantiation.cc
similarity index 100%
rename from libstdc++-v3/testsuite/20_util/unique_ptr/requirements/explicit_instantiation/explicit_instantiation.cc
rename to libstdc++-v3/testsuite/20_util/unique_ptr/requirements/explicit_instantiation.cc