[ez] Remove legacy float8 enabling flag in 405B toml (pytorch#559)

Somehow, when rebasing, the legacy float8 enabling flag stays in the
405B toml. Let's remove it. And this does not affect the perf number we
obtained because the old flag is just a no-op after rebase.

train_configs/llama3_405b.toml

@@ -33,7 +33,6 @@ max_norm = 1.0  # grad norm clipping
 steps = 3000
 data_parallel_degree = -1
 tensor_parallel_degree = 8  # 8-way TP
-enable_float8_linear = false
 compile = true
 dataset = "c4"