Remove CPU sample streaming support from the VM

[derekxu16]

This issue tracks the progress towards removing CPU sample streaming support from the VM. Note that the block-based sample buffer implementation must remain as-is, as stated in #61266 (comment). Changes related to this work that have already been landed at the time of opening this issue are:

[VM] Introduce --profile-startup CLI flag

Add --profile-startup flag to flutter run

[CPU Profiler] Delete the "Profile app start up" button