TRSS query should not have _xl in the plfatform

[llxia]

TKG queries TRSS for test execution time. The platform for aarch64_mac should not have _xl

00:02:11.422  Attempting to get test duration data from TRSS.
00:02:11.422  curl --silent --max-time 120 https://trssrtp1.fyre.ibm.com/api/getTestAvgDuration?limit=10&jdkVersion=11&impl=j9&platform=aarch64_mac_xl&group=functional&level=sanity

aarch64_mac test build x86-64_mac test build is correct.

source code: https://github.com/adoptium/TKG/blob/3ed8f8b66bc5ca5906e07efc7adf8abd74abe8fa/src/org/testKitGen/TestDivider.java#L228