Bump Security String to 2021-05-05

Implemented:
============
CVE:            References:  Type:  Severity:  Updated AOSP versions:
CVE-2021-0473   A-179687208  RCE    Critical   8.1, 9, 10, 11
CVE-2021-0474   A-177611958  RCE    Critical   8.1, 9, 10, 11
CVE-2021-0480   A-174493336  ID     High       8.1, 9, 10, 11
CVE-2021-0481   A-172939189  EoP    High       8.1, 9, 10, 11
CVE-2021-0484   A-173720767  ID     High       8.1, 9, 10, 11

Previously Implemented:
=======================
CVE:            References:  Type:  Severity:  Updated AOSP versions:  Prior Change:
CVE-2021-0477   A-178189250  EoP    High       8.1, 9, 10, 11          19db081e9bc9d

Not Implemented:
================
None

Not Applicable (platform source):
=================================
CVE:            References:  Type:  Severity:  Updated AOSP versions:
CVE-2019-2219   A-119041698  ID     High       11
CVE-2021-0466   A-154114734  ID     High       10
CVE-2021-0472   A-176801033  EoP    High       9, 10, 11
CVE-2021-0475   A-175686168  RCE    Critical   10, 11
CVE-2021-0476   A-169252501  EoP    High       9, 10, 11
CVE-2021-0482   A-173791720  EoP    High       11
CVE-2021-0485   A-174302616  EoP    High       11
CVE-2021-0487   A-174046397  EoP    High       11

Change-Id: Iad6ebf4c5b8c3de97a351a3fe01f7679807d7bd6