RFR: Remove redundant initialization code

[Aleksey Shipilev]

On Wed, 26 Apr 2023 16:13:35 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

> This code and the assertions that acompany it are subject to races with certain GC worker threads which are also capturing top_at_mark_start() and may capture it at a different position than this thread does.

I am actually surprised the allocation code does anything with TAMS. TAMS is supposed to be only updated by GC threads, well, _at mark start_ :) I see this reverts the relevant block almost to upstream state, so thumbs up.

-------------

Marked as reviewed by shade (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/267#pullrequestreview-1402358444