doc: strip build artefacts for examples file list

doc: strip build artefacts for examples file list

examples.dox is built inside builddir/doc/api and so doxygen generates
some dir_HASH.html that includes the builddir name and this may prevent
DPDK documentation to be correctly generated in some distributions, for
example CentOS Stream 9 and RHEL9, since the builddir includes the
architecture.

This commit adds builddir/doc/api (the path where examples.dox is
generated) to STRIP_FROM_PATH, so the generated documentation doesn't
change if builddir changes.

Fixes: a6090630f4e5 ("doc: automate examples file list for API")
Cc: stable@dpdk.org
Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Tested-by: David Marchand <david.marchand@redhat.com>