devtool: remove obsolete SRCTREECOVEREDTASKS handling

devtool: remove obsolete SRCTREECOVEREDTASKS handling

devtool modify generates a bbappend for kernel recipes which contains:
  SRCTREECOVEREDTASKS="\
    do_fetch \
    do_kernel_checkout \
    do_kernel_configcheck \
    do_unpack \
    do_validate_branches \
  "
  do_patch[noexec] = "1"

If the linux-yocto kernel is used, this is redundant. The
linux-yocto.bbclass already does the same:

linux-yocto sets SRCTREECOVEREDTASKS to
  SRCTREECOVEREDTASKS="\
    do_fetch \
    do_kernel_checkout \
    do_kernel_configcheck \
    do_patch \
    do_unpack \
    do_validate_branches \
  "

Also the do_patch[noexec] is redundant because the purpose of
SRCTREECOVEREDTASKS is to delete these tasks if the externalsrc.bbclass
is used.

The default value of SRCTREECOVEREDTASKS initialized in
externalsrc.bbclass is:
  SRCTREECOVEREDTASKS ?= "do_patch do_unpack do_fetch"
This is fine for kernels which do not inherit the linux-yocto.bbclass.

The code in devtool modify is redundant and therefore removed.

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>