sstate-cache-management.sh: Allow to remove old .siginfo and .done files for all tasks

* this allows to remove them even for tasks without sstate archives (e.g. rm_work, multilib_install, ..)
  whole list of tasks found in one of my sstate-cache directories:
  sstate:xxx_boostconfig.tgz ... 6
  sstate:xxx_bundle_initramfs.tgz ... 31
  sstate:xxx_compile.tgz ... 47894
  sstate:xxx_compile_kernelmodules.tgz ... 31
  sstate:xxx_compile_ptest_base.tgz ... 68
  sstate:xxx_configure.tgz ... 48247
  sstate:xxx_configure_ptest_base.tgz ... 68
  sstate:xxx_deploy.tgz ... 8
  sstate:xxx_evacuate_scripts.tgz ... 58
  sstate:xxx_fetch.tgz ... 7045
  sstate:xxx_generate.tgz ... 812
  sstate:xxx_generate_qt_config_file.tgz ... 576
  sstate:xxx_generate_toolchain_file.tgz ... 219
  sstate:xxx_install.tgz ... 48273
  sstate:xxx_install_locale.tgz ... 58
  sstate:xxx_install_ptest_base.tgz ... 68
  sstate:xxx_kernel_checkout.tgz ... 14
  sstate:xxx_kernel_configcheck.tgz ... 34
  sstate:xxx_kernel_configme.tgz ... 17
  sstate:xxx_kernel_link_vmlinux.tgz ... 30
  sstate:xxx_make_scripts.tgz ... 42
  sstate:xxx_multilib_install.tgz ... 29
  sstate:xxx_package.tgz ... 13848
  sstate:xxx_package_write_ipk.tgz ... 4615
  sstate:xxx_packagedata.tgz ... 4613
  sstate:xxx_pam_sanity.tgz ... 3
  sstate:xxx_patch.tgz ... 7883
  sstate:xxx_populate_adt.tgz ... 28
  sstate:xxx_populate_ide_support.tgz ... 33
  sstate:xxx_populate_lic.tgz ... 1718
  sstate:xxx_populate_sysroot.tgz ... 5094
  sstate:xxx_prepare_qmake_symlink.tgz ... 6
  sstate:xxx_prepsources.tgz ... 168
  sstate:xxx_rm_work.tgz ... 107630
  sstate:xxx_rm_work_all.tgz ... 52563
  sstate:xxx_rootfs.tgz ... 13
  sstate:xxx_sanitize_sources.tgz ... 8
  sstate:xxx_sizecheck.tgz ... 31
  sstate:xxx_strip.tgz ... 31
  sstate:xxx_uboot_mkimage.tgz ... 31
  sstate:xxx_unpack.tgz ... 7857
  sstate:xxx_unpack_extra.tgz ... 6
  sstate:xxx_validate_branches.tgz ... 14

* with this patches most of these files are removed as well
  Figuring out the sstate:xxx_compile ... (0 from 0 .tgz files for
  compile suffix will be removed or 42310 from 47795 when counting also
  .siginfo and .done files)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>