Cleanup: packet-context-field.c: logically dead code

Cleanup: packet-context-field.c: logically dead code

Coverity reported the following:
  CID 1401199 (#1 of 1): Logically dead code (DEADCODE)dead_error_begin:
  Execution cannot reach this statement: bt_field_wrapper_destroy

Reported-by: Coverity - 1401199 Logically dead code (DEADCODE)
Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: Ia53f46f998bcfb3a88f2d8a93343aa4c199a12ff
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2052
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>