[libc] Remove definition of LIBC_NAMESPACE in test (#86704)

The canonicalize test added in #85940 defined the LIBC_NAMESPACE macro.
this macro is intended to be set only by the build system and never in
the code.

GitOrigin-RevId: 4c72cfa31798a67c6daa25d474bcfe536e4fa0c0
1 file changed