Bump Security String to 2021-04-05

Implemented:
============
CVE:            References:  Type:  Severity:  Updated AOSP versions:
CVE-2021-0400   A-177561690  EoP    High       9, 10, 11
CVE-2021-0429   A-175074139  EoP    High       8.1, 9, 10, 11
CVE-2021-0431   A-174149901  ID     High       8.1, 9, 10, 11
CVE-2021-0433   A-171221090  EoP    High       8.1, 9, 10, 11
CVE-2021-0435   A-174150451  ID     High       8.1, 9, 10, 11
CVE-2021-0436   A-176496160  ID     High       8.1, 9, 10, 11
CVE-2021-0437   A-176168330  EoP    High       8.1, 9, 10, 11
CVE-2021-0438   A-152064592  EoP    High       8.1, 9, 10
CVE-2021-0443   A-170474245  ID     High       8.1, 9, 10, 11
CVE-2021-0444   A-178825358  ID     High       8.1, 9, 10, 11
CVE-2021-0445   A-172322502  EoP    High       9, 11
CVE-2021-0471   A-176444786  ID     High       8.1, 9, 10, 11

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

Not Applicable (platform source):
=================================
CVE:            References:  Type:  Severity:  Updated AOSP versions:
CVE-2021-0426   A-174485572  EoP    High       11
CVE-2021-0427   A-174488848  EoP    High       11
CVE-2021-0428   A-173421434  ID     High       10
CVE-2021-0430   A-178725766  RCE    Critical   10, 11
CVE-2021-0432   A-173552790  EoP    High       11
CVE-2021-0439   A-174243830  EoP    High       11
CVE-2021-0442   A-174768985  EoP    High       11
CVE-2021-0446   A-172252122  EoP    High       11

Change-Id: I91e9c3b5cc8b660835dd59d10230233bb24b24ea