[honeydew][serial] Merge Mobly serial test targets

Simplifies the GN configuration by merging individual
test case targets into a single serial_test target.

Bug: 483812907
Depends-On: turquoise-internal:I2b8ae089332b774710b0b1f8b9b90fdd414bb394
Change-Id: I1849658dcd229a4e8541be1852962da54b1db172
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1503698
Reviewed-by: Cole Alban <colealban@google.com>
Reviewed-by: Pavan Kumar Juturu <jpavankumar@google.com>
Dependencies-Satisfied: CL Deps Checker <cl-deps-checker@fuchsia-internal-service-accts.iam.gserviceaccount.com>
Commit-Queue: Pavan Kumar Juturu <jpavankumar@google.com>
Fuchsia-Auto-Submit: Pavan Kumar Juturu <jpavankumar@google.com>