MINOR: tinfo: remove the global thread ID bit (tid_bit)

MINOR: tinfo: remove the global thread ID bit (tid_bit)

Each thread has its own local thread id and its own global thread id,
in addition to the masks corresponding to each. Once the global thread
ID can go beyond 64 it will not be possible to have a global thread Id
bit anymore, so better start to remove it and use only the local one
from the struct thread_info.