kallsyms: Revert "Take callthunks into account"

This is a full revert of commit:

  f1389181 ("kallsyms: Take callthunks into account")

The commit assumes a number of things that are not quite right.
Notably it assumes every symbol has PADDING_BYTES in front of it that
are not claimed by another symbol.

This is not true; even when compiled with:

  -fpatchable-function-entry=${PADDING_BYTES},${PADDING_BYTES}

Notably things like .cold subfunctions do not need to adhere to this
change in ABI. It it also not true when build with CFI_CLANG, which
claims these PADDING_BYTES in the __cfi_##name symbol.

Once the prefix bytes are not consistent and or otherwise claimed the
approach this patch takes goes out the window and kallsym resolution
will report invalid symbol names.

Therefore revert this to make room for another approach.

Reported-by: Reported-by: kernel test robot <yujie.liu@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Yujie Liu <yujie.liu@intel.com>
Link: https://lore.kernel.org/r/202210241614.2ae4c1f5-yujie.liu@intel.com
Link: https://lkml.kernel.org/r/20221028194453.330970755@infradead.org