define STREQ(a,b) consistently, removing useless parentheses

define STREQ(a,b) consistently, removing useless parentheses

#define STREQ(a, b) (strcmp ((a), (b)) == 0) is over-parenthesized,
since the only risk is that "a" or "b" contains an unparenthesized
comma, but if either did that, STREQ would have 3 or more arguments.
Hence, #define STREQ(a, b) (strcmp (a, b) == 0) is better.
* lib/fts.c (STREQ): Remove unnecessary parentheses.
* lib/hash-triple.c (STREQ): Likewise.
* tests/test-argv-iter.c (STREQ): Use a and b, not s1 and s2.
* lib/getugroups.c (STREQ): Likewise.