Stop removing the Autoconf cache after autoreconf

No need to do this any more.

.gitignore

 /Makefile.in
 /aclocal.m4
+/autom4te.cache/
 /build-aux/
 /client/wallet
 /client/wallet-rekey

autogen

@@ -4,8 +4,8 @@
 
 set -e
 
+# Regenerate all the autotools files.
 autoreconf -i --force
-rm -rf autom4te.cache
 
 # Generate manual pages.
 version=`grep '^wallet' NEWS | head -1 | cut -d' ' -f2`