grammar: do not add a \n at the end of blocks of code

Now that we use "braceless" (which is {...} blocks of code with
initial and final braces stripped) to denote "short" values (such as
api.namespaces), the added end-of-line is a nuisance.  As a matter of
fact, this extra-safety was useless, as every expansion of "braceless"
(aka, "user code") is followed by an end of line.

* src/parse-gram.y, src/parse-gram.c (braceless): Instead of replacing
the final brace by \n, just delete the brace.