doc: drop unused tex files

Remove tex header templates only used in latex document generation.
Clarify the HACKING document to reflect no pdf/latex

Fixes: 9443856b doc: drop latex support

doc/sam3a/header_sam3a.tex

@@ -1,61 +0,0 @@
-\documentclass{book}
-\usepackage[a4paper,top=2.5cm,bottom=2.5cm,left=2.5cm,right=2.5cm]{geometry}
-\usepackage{makeidx}
-\usepackage{natbib}
-\usepackage{graphicx}
-\usepackage{multicol}
-\usepackage{float}
-\usepackage{listings}
-\usepackage{color}
-\usepackage{ifthen}
-\usepackage[table]{xcolor}
-\usepackage{textcomp}
-\usepackage{alltt}
-\usepackage{ifpdf}
-\ifpdf
-\usepackage[pdftex,
-            pagebackref=true,
-            colorlinks=true,
-            linkcolor=blue,
-            unicode
-           ]{hyperref}
-\else
-\usepackage[ps2pdf,
-            pagebackref=true,
-            colorlinks=true,
-            linkcolor=blue,
-            unicode
-           ]{hyperref}
-\usepackage{pspicture}
-\fi
-\usepackage[utf8]{inputenc}
-\usepackage{mathptmx}
-\usepackage[scaled=.90]{helvet}
-\usepackage{courier}
-\usepackage{sectsty}
-\usepackage{amssymb}
-\usepackage[titles]{tocloft}
-\usepackage{doxygen}
-\lstset{language=C++,inputencoding=utf8,basicstyle=\footnotesize,breaklines=true,breakatwhitespace=true,tabsize=4,numbers=left }
-\makeindex
-\setcounter{tocdepth}{3}
-\renewcommand{\footrulewidth}{0.4pt}
-\renewcommand{\familydefault}{\sfdefault}
-\hfuzz=15pt
-\setlength{\emergencystretch}{15pt}
-\hbadness=750
-\tolerance=750
-\begin{document}
-\hypersetup{pageanchor=false,citecolor=blue}
-\begin{titlepage}
-\vspace*{7cm}
-\begin{center}
-{\Huge libopencm3: API Reference\\ Atmel SAM3A ARM Cortex M3 Series}\\
-\vspace*{1cm}
-{\large Generated by Doxygen 1.8.2}\\
-\vspace*{0.5cm}
-{\small Thu Sep 13 2012 23:26:45}\\
-\end{center}
-\end{titlepage}
-\pagenumbering{arabic}
-\hypersetup{pageanchor=true,citecolor=blue}