Removed _xl for mac platform in TRSS query

[annaibm]

• The platform for aarch64_mac should not include _xl in TRSS url when querying for test execution times,
• Adjusted the code to remove _xl from the platform string if the OS is macOS.

related: https://github.com/adoptium/TKG/issues/557

[annaibm]

Grinder links: aarch64_mac https://hyc-runtimes-jenkins.swg-devops.com/job/Grinder/42694/ x86-64_mac https://hyc-runtimes-jenkins.swg-devops.com/job/Grinder/42695/