notes merge: eliminate OUTPUT macro

notes merge: eliminate OUTPUT macro

The macro is variadic, which breaks support for pre-C99 compilers,
and it hides an "if", which can make code hard to understand on
first reading if some arguments have side-effects.

The OUTPUT macro seems to have been inspired by the "output" function
from merge-recursive.  But that function in merge-recursive exists to
indent output based on the level of recursion and there is no similar
justification for such a function in "notes merge".

Noticed with 'make CC="gcc -std=c89 -pedantic"':

 notes-merge.c:24:22: warning: anonymous variadic macros were introduced in C99 [-Wvariadic-macros]

Encouraged-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>