Reproduction steps:
1. Open the attached user's project "ProfilerFrameData.zip"
2. Open the Profiler, make sure the record button is not selected and select Deep Profiler and Profile Editor
3. Press record and let the Profiler capture some data but don't let it fill the whole window
4. Press clear after captured data is halfway across the Profiler and stop the recording
5. Select the Hierarchy in the Profiler and search for ProfilerFrameData.DeleteThreadData in the Profiler search field
6. Select the ProfilerFrameData.DeleteThreadData in the Hierarchy and look for the peak near the start of the newly captured data

Expected result: ProfilerFrameData.DeleteThreadData does not generate significant stalls in 1 frame on the main thread when Deep Profiling
Actual result: ProfilerFrameData.DeleteThreadData generates significant stalls in 1 frame on the main thread when Deep Profiling (See attached ProfilerData.mp4)

Reproduces on: 2018.4.24f1, 2019.3.16f1, 2019.4.3f1, 2020.1.0b15, 2020.2.0a17

Notes:
- This issue generates a considerable stall when hitting clear, even on an empty project without entering play mode.
- The main issue is that this will occur when "Clear On Play" is on when entering play mode.