shared: drop UNIQUE()

shared: drop UNIQUE()

The UNIQUE() macro works fine if used in un-stacked macros. However, once
you stack them like:
        MAX(MIN(a, b),
            CLAMP(MAX(c, d), e, f))
you will get warnings due to shadowing other variables. gcc uses the last
line of a macro expansion as value for __LINE__, therefore, we cannot even
avoid this by splitting the expressions across lines.

Remove the only user of UNIQUE() so we introduce a new helper in
follow-ups.