PR libstdc++/83626 Don't throw for remove("") and remove_all("")

PR libstdc++/83626 Don't throw for remove("") and remove_all("")

	PR libstdc++/83626
	* src/filesystem/ops.cc (remove(const path&, error_code&))): Remove
	redundant call to ec.clear().
	(remove_all(const path&, error_code&))): Do not return an error for
	non-existent paths.
	* src/filesystem/std-ops.cc: Likewise.
	* testsuite/27_io/filesystem/operations/remove.cc: New test.
	* testsuite/27_io/filesystem/operations/remove_all.cc: Fix expected
	results for non-existent paths.
	* testsuite/experimental/filesystem/operations/remove.cc: New test.
	* testsuite/experimental/filesystem/operations/remove_all.cc: Fix
	expected results for non-existent paths.

From-SVN: r256269