Remove redundant C locale settings.

Various glibc build / install / test code has C locale settings that
are redundant with LC_ALL=C.

LC_ALL takes precedence over LANG, so anywhere that sets LC_ALL=C
(explicitly, or through it being in the default environment for
running tests) does not need to set LANG=C.  LC_ALL=C also takes
precedence over LANGUAGE, since

2001-01-02  Ulrich Drepper  <drepper@redhat.com>

	* intl/dcigettext.c (guess_category_value): Rewrite so that LANGUAGE
	value is ignored if the selected locale is the C locale.
	* intl/tst-gettext.c: Set locale for above change.
	* intl/tst-translit.c: Likewise.

and so settings of LANGUAGE=C are also redundant when LC_ALL=C is
set.  One test also had LC_ALL=C in its -ENV setting, although it's
part of the default environment used for tests.

This patch removes the redundant settings.  It removes a suggestion in
install.texi of setting LANGUAGE=C LC_ALL=C for "make install"; the
Makefile.in target "install" already sets LC_ALL_C so there's no need
for the user to set it (and nor should there be any need for the user
to set it).

If some build machine tool used by "make install" uses a version of
libintl predating that 2001 change, and the user has LANGUAGE set, the
removal of LANGUAGE=C from the Makefile.in "install" rule could in
principle affect the user's installation.  However, I don't think we
need to be concerned about pre-2001 build tools.

Tested x86_64.

	* Makefile (install): Don't set LANGUAGE.
	* Makefile.in (install): Likewise.
	* assert/Makefile (test-assert-ENV): Remove variable.
	(test-assert-perr-ENV): Likewise.
	* elf/Makefile (neededtest4-ENV): Likewise.
	* iconvdata/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Don't set LANGUAGE.
	* io/ftwtest-sh (LANG): Remove variable.
	* libio/Makefile (tst-widetext-ENV): Likewise.
	* manual/install.texi (Running make install): Don't refer to
	environment settings for make install.
	* INSTALL: Regenerated.
	* nptl/tst-tls6.sh: Don't set LANG.
	* posix/globtest.sh (LANG): Remove variable.
	* string/Makefile (tester-ENV): Likewise.
	(inl-tester-ENV): Likewise.
	(noinl-tester-ENV): Likewise.
	* sysdeps/s390/s390-64/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Don't set LANGUAGE.
	* timezone/Makefile (build-testdata): Use $(built-program-cmd)
	without explicit environment settings.

localedata/ChangeLog:
	* tst-fmon.sh: Don't set LANGUAGE.
	* tst-locale.sh: Likewise.