twister: size_calc: Remove stale k_mem_pool_area reference

This commit removes the stale reference to `k_mem_pool_area` for the
memory pool API, which was removed in the v2.5.0 release.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

scripts/pylib/twister/twisterlib/size_calc.py

@@ -27,7 +27,6 @@ class SizeCalculator:
         "_static_thread_data_area",
         "k_timer_area",
         "k_mem_slab_area",
-        "k_mem_pool_area",
         "sw_isr_table",
         "k_sem_area",
         "k_mutex_area",