hooks: cleanup the correct doc folders

[Meulengracht]

fixes the remaining listed slices in the manifest: #443

Before fix:

[philip@philip-ws squashfs-root]$ find . -name libgnutls*
./usr/lib/x86_64-linux-gnu/libgnutls.so.30
./usr/lib/x86_64-linux-gnu/libgnutls.so.30.41.1
./usr/share/doc/libgnutls-dane0t64
./usr/share/doc/libgnutls30t64
[philip@philip-ws squashfs-root]$ find . -name libevent*
./usr/share/doc/libevent-2.1-7t64
[philip@philip-ws squashfs-root]$ find . -name libmagic*
./usr/share/doc/libmagic1t64

After fix:

[philip@philip-ws squashfs-root]$ find . -name libgnutls*
./usr/lib/x86_64-linux-gnu/libgnutls.so.30
./usr/lib/x86_64-linux-gnu/libgnutls.so.30.41.1
./usr/share/doc/libgnutls30t64
[philip@philip-ws squashfs-root]$ find . -name libevent*
[philip@philip-ws squashfs-root]$ find . -name libmagic*
[philip@philip-ws squashfs-root]$ 


[philip@philip-ws chisel]$ cat manifest.json | grep libmagic
[philip@philip-ws chisel]$ cat manifest.json | grep libevent
[philip@philip-ws chisel]$ cat manifest.json | grep libgnutls-dane
[philip@philip-ws chisel]$