Update build_style for all templates.

- There's no need to set build_style for custom-install (default).
- gnu_{configure,makefile} renamed to gnu-{configure,makefile}.

srcpkgs/btrfs-progs/template

@@ -2,7 +2,7 @@
 pkgname=btrfs-progs
 version=20101110
 distfiles="http://xbps.nopcode.org/distfiles/$pkgname-$version.tar.gz"
-build_style=gnu_makefile
+build_style=gnu-makefile
 make_build_args="CFLAGS=-Wno-error"
 make_install_args="prefix=/usr bindir=/sbin mandir=/usr/share/man"
 short_desc="Btrfs filesystem utilities"