Update install.texi documentation of uses of Perl and Python.

Update install.texi documentation of uses of Perl and Python.

The install.texi documentation of uses of Perl and Python is
substantially out of date.

The description of Perl is "to test the installation" (which I
interpret as referring to test-installation.pl), but it's used for
more tests than that, and to build the manual, and to regenerate one
file in the source tree.

The description of Python is only for pretty-printer tests, but it's
used for other tests / benchmarks as well (and for other internal uses
such as updating Unicode data, for which we already require Python 3,
but I think install.texi only needs to describe uses from the main
glibc Makefiles).

This patch updates the descriptions of what those tools are used for.
The Python information (and information about other tools for testing
pretty printers) was awkwardly in the middle of the general
description of building and testing glibc, rather than with the rest
of information about tools used in glibc build and test; this patch
moves the information about those tools into the main list.

Tested with regeneration of INSTALL as well as "make info" and "make
pdf".

	* manual/install.texi (Configuring and compiling): Do not list
	tools used for testing pretty printers here.
	(Tools for Compilation): List Python, PExpect and GDB here.
	Update descriptions of uses of Perl and Python.
	* INSTALL: Regenerate.