Change two tests to be less dependant on locales.

This patch removes the use of the "%c" specifier for getting/setting times.
The semantics of this specifier differ between linux and Mac. I don't believe
the use of this specifier was important to the test.

The following tests now pass on linux.
test/input.output/iostream.format/ext.manip/get_time.pass.cpp
test/input.output/iostream.format/ext.manip/put_time.pass.cpp

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@215417 91177308-0d34-0410-b5e6-96231b3b80d8