gdb/mi: Remove extra \n from tsv and and traceframe notifications

gdb/mi: Remove extra \n from tsv and and traceframe notifications

An extra \n in calls to fprintf_unfiltered() caused invalid MI records
to be emitted:

   > gdb -i mi3 -ex "target remote :7000"
   =thread-group-added,id="i1"
   ~"GNU gdb (GDB) 11.0.50.20201019-git\n"
   ~"Copyright (C) 2020 Free Software Foundation, Inc.\n"
   ...
   ~"Remote debugging using :7001\n"
   =tsv-created,name="trace_timestamp",initial="0"\n
   =thread-group-started,id="i1",pid="304973"

This commit fixes the problem.

gdb/ChangeLog:

        * gdb/mi/mi-interp.c (mi_traceframe_changed): Remove trailing \n from output.
        (mi_tsv_created): Likewise.
        (mi_tsv_deleted): Likewise.