chore: Remove Email model

[markstory]

The Email model and writes (via signal handlers) was added back in 2017, but there have never been any reads to the table in either sentry, getsentry or internal etl pipelines.

This table is often missing records which cause relocation validation failures. Removing this table will reduce our write throughput and simplify the user datamodel.

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1101_remove_email_model_pending.py

for 1101_remove_email_model_pending in sentry

--
-- Moved model Email to pending deletion state
--
-- (no-op)

[github-actions]

Backend Test Failures

Failures on 452a31f in this run:

tests/sentry/backup/test_validate.py::test_good_user_custom_ordinal — log

[gw0] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/backup/test_validate.py:793: in test_good_user_custom_ordinal
    out = validate(left, right)
          ^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:173: in validate
    left_models, left_ordinal_counters = build_model_map(left_data, Side.left, findings)
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:98: in build_model_map
    raise RuntimeError("Unknown model class")
E   RuntimeError: Unknown model class

tests/sentry/backup/test_validate.py::test_auto_assign_email_obfuscating_comparator — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/backup/test_validate.py:287: in test_auto_assign_email_obfuscating_comparator
    out = validate(left, right)
          ^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:173: in validate
    left_models, left_ordinal_counters = build_model_map(left_data, Side.left, findings)
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:98: in build_model_map
    raise RuntimeError("Unknown model class")
E   RuntimeError: Unknown model class

tests/sentry/backup/test_validate.py::test_bad_missing_custom_ordinal — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/backup/test_validate.py:524: in test_bad_missing_custom_ordinal
    out = validate(left, right)
          ^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:173: in validate
    left_models, left_ordinal_counters = build_model_map(left_data, Side.left, findings)
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
src/sentry/backup/validate.py:98: in build_model_map
    raise RuntimeError("Unknown model class")
E   RuntimeError: Unknown model class