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/screen/template

@@ -3,7 +3,7 @@ pkgname=screen
 version=4.0.3
 revision=4
 distfiles="http://ftp.gnu.org/gnu/$pkgname/$pkgname-$version.tar.gz"
-build_style=gnu_configure
+build_style=gnu-configure
 configure_args="--with-sys-screenrc=/etc/screenrc -enable-pam --enable-colors256"
 short_desc="The GNU screen utility"
 maintainer="davehome <davehome@redthumb.info.tm>"