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/ffmpeg/template

@@ -3,7 +3,6 @@ pkgname=ffmpeg
 version=0.7.6
 homepage="http://www.ffmpeg.org"
 distfiles="${homepage}/releases/ffmpeg-${version}.tar.bz2"
-build_style=custom-install
 short_desc="Decoding, encoding and streaming software"
 maintainer="Juan RP <xtraeme@gmail.com>"
 license="GPL-3"