ArmPkg/TimerDxe: remove workaround for KVM timer handling

When we first ported EDK2 to KVM/arm, we implemented a workaround for
the quirky timer handling on the KVM side. This has been fixed in
Linux commit f120cd6533d2 ("KVM: arm/arm64: timer: Allow the timer to
control the active state") dated 23 June 2014, which was incorporated
into Linux release 4.3.

So almost 4 years later, it should be safe to drop this workaround on
the EDK2 side.

This reverts commit b1a633434ddc.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>