Disable Gnulib’s non-Gregorian calendars

Prepare for the next Gnulib merge by disabling the optional
support for non-Gregorian calendars recently added to Gnulib’s
nstrftime module.  This would be tricky to integrate with Emacs,
as Emacs has its own (much fancier) calendar system, one that at
least for the Persian calendar sometimes disagrees with Gnulib’s,
and it’s likely not worth the trouble of reconciling the conflicts.
* src/conf_post.h (SUPPORT_NON_GREG_CALENDARS_IN_STRFTIME):
New macro, defined to false.
* admin/merge-gnulib (GNULIB_MODULES): nstrftime → nstrftime-limited.
(AVOIDED_MODULES): Add localcharset.
Near the end, also remove the files lib/calendar-ethiopian.h,
lib/calendar-persian.h, lib/calendar-thai.h, lib/calendars.h.

admin/merge-gnulib

@@ -43,7 +43,7 @@ GNULIB_MODULES='
   ieee754-h ignore-value intprops largefile libgmp lstat
   malloc-gnu manywarnings memmem-simple mempcpy memrchr memset_explicit
   minmax mkostemp mktime
-  nanosleep nproc nstrftime
+  nanosleep nproc nstrftime-limited
   pathmax pipe2 pselect pthread_sigmask
   qcopy-acl readlink readlinkat realloc-posix regex
   sig2str sigdescr_np socklen stat-time std-gnu11
@@ -58,7 +58,7 @@ GNULIB_MODULES='
 AVOIDED_MODULES='
   access btowc chmod close crypto/af_alg dup fchdir fstat gnulib-i18n
   iswblank iswctype iswdigit iswxdigit langinfo-h libgmp-mpq
-  locale-h localename-unsafe-limited lock
+  localcharset locale-h localename-unsafe-limited lock
   mbrtowc mbsinit memchr mkdir msvc-inval msvc-nothrow nl_langinfo
   openat-die opendir pthread-h raise
   save-cwd select setenv sigprocmask stat stdarg-h
@@ -140,7 +140,11 @@ fi
 
 "$gnulib_srcdir"/gnulib-tool --dir="$src" $GNULIB_TOOL_FLAGS \
 	$avoided_flags $GNULIB_MODULES &&
-rm -- "$src"lib/gl_openssl.h \
+rm -- "$src"lib/calendar-ethiopian.h \
+      "$src"lib/calendar-persian.h \
+      "$src"lib/calendar-thai.h \
+      "$src"lib/calendars.h \
+      "$src"lib/gl_openssl.h \
       "$src"lib/stdio-read.c "$src"lib/stdio-write.c \
       "$src"m4/fcntl-o.m4 \
       "$src"m4/gl-openssl.m4 \