Remove the deprecated and unused legacy_tap_project_id field.  Additionally, if legacy_tap_project_id is the only field set in the tap_settings field, remove it too.

More information:
- http://go/legacy_tap_project_id_lsc

Tested:
TAP --sample for global presubmit queue
http://test/OCL:78864164:BASE:78867616:1414699790379:43d3bb0c

R=ozarov
DELTA=2 (0 added, 1 deleted, 1 changed)

Revision created by MOE tool push_codebase.
MOE_MIGRATION=7160