test: clear flaky designation for test-stream-pipeline-http2

It hasn't failed for a long time.

Closes: #20750

PR-URL: #37631
Fixes: #20750
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ruy Adorno <ruyadorno@github.com>

Author: Trott

test/parallel/parallel.status

@@ -7,8 +7,6 @@ prefix parallel
 [true] # This section applies to all platforms
 
 [$system==win32]
-# https://github.com/nodejs/node/issues/20750
-test-stream-pipeline-http2: PASS,FLAKY
 # https://github.com/nodejs/node/issues/24497
 test-timers-immediate-queue: PASS,FLAKY
 # https://github.com/nodejs/node/issues/23277