remove code forcing testsets to be compiled (#34405)

stdlib/Test/src/Test.jl

@@ -1101,9 +1101,6 @@ function testset_beginend(args, tests, source)
     ex = quote
         _check_testset($testsettype, $(QuoteNode(testsettype.args[1])))
         local ts = $(testsettype)($desc; $options...)
-        # this empty loop is here to force the block to be compiled,
-        # which is needed for backtrace scrubbing to work correctly.
-        while false; end
         push_testset(ts)
         # we reproduce the logic of guardseed, but this function
         # cannot be used as it changes slightly the semantic of @testset,

stdlib/Test/test/runtests.jl

@@ -607,8 +607,6 @@ end
     end
     """)
     local msg = read(pipeline(ignorestatus(`$(Base.julia_cmd()) --startup-file=no --color=no $f`), stderr=devnull), String)
-    # NOTE: This test depends on the code generated by @testset getting compiled,
-    # to get good backtraces. If it fails, check the implementation of `testset_beginend`.
     @test !occursin("do_test(", msg)
     @test !occursin("include(", msg)
     @test occursin("at " * f * ":3", msg)