BACKPORT: arm64: asm-offsets: remove unused definitions

Subsequent patches will move the thread_info::{task,cpu} fields, and the
current TI_{TASK,CPU} offset definitions are not used anywhere.

This patch removes the redundant definitions.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit 3fe12da4c7fa6491e0fb7c5371716ac7f8ea80a5)

Change-Id: I1753d6ba7db05c1395315b6956af500a32c9e426
[ghackmann@google.com: fix trivial merge conflicts with SW PAN emulation
 backport]
Signed-off-by: Greg Hackmann <ghackmann@google.com>