Review .gitignore files contents

Review .gitignore files contents

* Move entries belonging to src/ into src/.gitignore.
* Drop lines for files inside build-aux/ since that is ignored already.
* No need to ignore src/Makefile.in, the entry 'Makefile.in' catches
  that already.
* Remove entry for '.*.d', (recent?) autotools doesn't create any
  matching files.
* Drop entries for non-existent parser.c and parser.h files.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>