ondevice-signing: merge createCertificate() into createSelfSignedCertificate()

Since createSelfSignedCertificate() is now the only caller of
createCertificate(), merge createCertificate() into it.

Bug: 290064770
Test: atest odsign_e2e_tests_full
Change-Id: Id970743f1a3f3a3b7dd8a81da56c1e7b40959423
1 file changed