allarch.bbclass: Exclude package_do_shlibs from do_package signature
shlibs is largely useless for allarch, the particular usecase where it
fails is when DISTRO_FEATURE is changing due to libc being different e.g.
Variable package_do_shlibs value changed:
-DISTRO_FEATURES{ldconfig} = Set
+DISTRO_FEATURES{ldconfig} = Unset
musl -> glibc or other way around 'ldconfig' gets added or deleted to
DISTRO_FEATURE set, neither this distro feature nor the shlibs processing
during packaging is of interest to allarch packages which are largely
arch independent scripts
