restore build with --enable-maintainer-mode

A build with --enable-maintainer-mode is currently failing with:

make[4]: *** No rule to make target '<SRC>/gas/config/te-ia64aix.h',
	 needed by '<SRC>/gas/po/gas.pot'.  Stop.
make[4]: Leaving directory '<$OBJ>/gas/po'
make[3]: *** [Makefile:1695: all-recursive] Error 1
...

As config/te-ia64aix.h is now removed, remove the corresponding fragment
from the makefile.

gas/
        * Makefile.am: Remove config/te-ia64aix.h.
        * Makefile.in: Regenerate.
        * po/POTFILES.in: Regenerate.

gas/Makefile.am

@@ -342,7 +342,6 @@ TARG_ENV_HFILES = \
 	config/te-hppa.h \
 	config/te-hppa64.h \
 	config/te-hppalinux64.h \
-	config/te-ia64aix.h \
 	config/te-interix.h \
 	config/te-lynx.h \
 	config/te-macos.h \

gas/Makefile.in

@@ -841,7 +841,6 @@ TARG_ENV_HFILES = \
 	config/te-hppa.h \
 	config/te-hppa64.h \
 	config/te-hppalinux64.h \
-	config/te-ia64aix.h \
 	config/te-interix.h \
 	config/te-lynx.h \
 	config/te-macos.h \

gas/po/POTFILES.in

@@ -204,7 +204,6 @@ config/te-go32.h
 config/te-hppa.h
 config/te-hppa64.h
 config/te-hppalinux64.h
-config/te-ia64aix.h
 config/te-interix.h
 config/te-lynx.h
 config/te-macos.h