Revert "AOSP/UnifiedEmail - Bumped the targetSdkVersion to 28 (maximum version). Used JobIntentservice API calls to replace context.startService."

This reverts commit c851a0a2fa18cf76f4fe5eb53ce489f051fb7019.

Reason for revert: No notification when new email arrived
Bug: 132923014

Cherry picking - https://android-review.googlesource.com/c/platform/packages/apps/UnifiedEmail/+/990099

Test: manual - Ran the following tests on Pixel phone. Tested the email UI for notification.

$ make -j 40
$ make EmailTests -j
$ adb install -r out/target/product/marlin/system/product/app/Email/Email.apk
$ adb install -r out/target/product/marlin/testcases/EmailTests/arm64/EmailTests.apk

$ adb shell am instrument -w com.android.email.tests
  Time: 2.986
  OK (157 tests)

Change-Id: I010565b2f8616195f397db4473b3a34fc8b150b5
Merged-In: I010565b2f8616195f397db4473b3a34fc8b150b5
4 files changed