ACPICA: Drop stale comment about the header file content

ACPICA commit 48e7c4cd893270dab8d05e6d75fbf23d0fcbb267

Commit a025731aec31 ("Restructure ACPI table files") restructed the
header files and moved lots of tables that are in the ACPI specification
to actbl2.h(e.g.: APIC/MADT, PCCT, PPTT, ..etc).

This restructure made the comment stating this header file contains tables
that are not in the ACPI specification incorrect. From that commit onwards
it has remained as stale. Let us get rid of it as it might be misleading.

Link: https://github.com/acpica/acpica/commit/48e7c4cd


Reported-by: Sahil Kaushal <sahil.kaushal@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/6168200.lOV4Wx5bFT@rjwysocki.net