vendor/lineage: Remove kernel.mk headers generation

*) This has been deprecated by the bp mobule
   generated_kernel_headers.

*) To build with kernel headers, do this:
   LOCAL_HEADER_LIBRARIES += generated_kernel_headers
   Or for soong targets:
   header_libs: [ "generated_kernel_headers" ],

Change-Id: Idad445709f0ee0ec11b41b40123b14976a0052ad