sstate: replace verbose manifest removal with a single count
If there are lots of changes between the previous build and the build about to
start bitbake will potentially print pages of:
DEBUG: Stamp $BUILD/stamps/corei7-64-poky-linux/libdrm/2.4.66-r0 is not reachable, removing related manifests
Instead of spamming the console with this list, write the list of manifests only
to the debug log and simply write a count to the console. This way the user
doesn't get spammed but still knows what is happening if bitbake appears to
stall with heavy I/O.
Signed-off-by: Ross Burton <ross.burton@intel.com>
