target: msm8974: Remove unused panel signature API definition
target: msm8974: Remove unused panel signature API definition

Remove the unused implementation of panel signature read API in 8974
as shared code already has this.

Change-Id: Idfed1de61ff3355ec8a811fcffa1f0e5e198eb40

Redmi-dev/android_bootable_lk,Redmi-dev/android_bootable_lk,t2m-foxfone/kernel_lk,mozilla-b2g/kernel_lk,mozilla-b2g/kernel_lk,mozilla-b2g/kernel_lk,mozilla-b2g/kernel_lk,t2m-foxfone/kernel_lk,t2m-foxfone/kernel_lk,t2m-foxfone/kernel_lk,Redmi-dev/android_bootable_lk,mozilla-b2g/kernel_lk,Redmi-dev/android_bootable_lk,t2m-foxfone/kernel_lk,Redmi-dev/android_bootable_lk