dependencies: remove a few useless mandatory dependencies

awk, bison, flex, makeinfo, gettext should be built as dependencies of
packages when needed. In practice, even the toolchain build doesn't
need any of these, and only a few packages do require them.

It is not needed to list gzip and bzip2 since they are already checked
through ${DL_TOOLS}: whenever a package needs gzip or bzip2 for its
extraction, the dependency is added.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/manual/prerequisite.txt

@@ -30,10 +30,6 @@ Mandatory packages
 ** +gcc+ (version 2.95 or any later)
 ** `g++` (version 2.95 or any later)
 ** +bash+
-** +gawk+
-** +bison+
-** +flex+
-** +gettext+
 ** +patch+
 ** +gzip+
 ** +bzip2+
@@ -43,7 +39,6 @@ Mandatory packages
 ** +python+ (version 2.6 or 2.7)
 ** +unzip+
 ** +rsync+
-** +texinfo+ (required for internal Buildroot toolchain backend)
 
 * Source fetching tools:
 ** +wget+