Revert "It can be like this. An optional type after []."

This reverts commit cada5b7e2305734efaadb35edd8c0b8f5f466204.

Conflicts:
	src/cmd/gc/y.tab.c
Add bison warnings. Remove useless %left. Change to %precedence.
Make it like this to be yacc-compatible.
Reset the grammar stuff back to master
We add the optional slice type to the grammar like this.

Now the grammar seems good and the demos run.