remove forgotten config.cache residue from last commit

gdb/gdb.spec

@@ -84,7 +84,6 @@ AutoReqProv:  no
     LIBS="%{l_ldflags} -liconv" \
     ./configure \
         --prefix=%{l_prefix} \
-        --cache-file=./config.cache \
         --with-libiconv-prefix=%{l_prefix} \
         --disable-nls
     cd ..