Log Message:
firefox68: Update to 68.6.0

While here,

- Remove OSS support now that cubeb_sun has been stable for a long while
- Appease pkglint

Security fixes in this release:

#CVE-2020-6805: Use-after-free when removing data about origins
#CVE-2020-6806: BodyStream::OnInputStreamReady was missing protections
#CVE-2020-6807: Use-after-free in cubeb during stream destruction
#CVE-2020-6811: Devtools' 'Copy as cURL' feature did not fully escape
#CVE-2019-20503: Out of bounds reads in sctp_load_addresses_from_init
#CVE-2020-6812: The names of AirPods with personally identifiable
#CVE-2020-6814: Memory safety bugs fixed in Firefox 74 and Firefox ESR 68.6