Revert^2 "Wait for thread termination in PreZygoteFork()"

Revert of 02285d918d3ab1e95fe1849842661bdf194294c9

PS1 is identical to aosp/2782117

PS2 no longer erroneously passes null as self.

Bug: 299221079
Bug: 304183774
Test: Build and boot AOSP, TreeHugger
(cherry picked from https://android-review.googlesource.com/q/commit:7d6bd10f0a2c3fd0b81e33d1d61ca60a0ecaae11)
Merged-In: Iaf8c26208c71c6a5dcb46a2eb0472f572cf4099a
Change-Id: Iaf8c26208c71c6a5dcb46a2eb0472f572cf4099a