tests: thrift: Remove 'newlib' from test identifiers

The Thrift module tests were under the "newlib" namespace, presumably
because newlib was the default at the time of their introduction.

Since newlib is no longer the default libc and Thrift is not being tested
against multiple C libraries, this removes the libc type from the Thrift
test identifiers.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>