btrfs-progs: autoconf: use standard PACKAGE_* macros

btrfs-progs: autoconf: use standard PACKAGE_* macros

- use standard PACKAGE_{NAME,VERSION,STRING,URL,...} autoconf macros
  rather than homemade BTRFS_BUILD_VERSION

- don't #include version.h, now the file is necessary for library API only

Note that "btrfs version" returns "btrfs-progs <version>" instead of
the original confusing "btrfs <version>".

Signed-off-by: Karel Zak <kzak@redhat.com>
Signed-off-by: David Sterba <dsterba@suse.cz>