Avoid needless local variables in Python wrappers

[eerovaher]

The Python wrappers that can simply return the corresponding ufunc's return value no longer store the ufunc's output in local variables, which makes them slightly faster. For example, on current main

$ ipython -i -c 'from erfa import epb2jd, zp'
Python 3.11.12 (main, May 17 2025, 13:48:36) [Clang 20.1.4 ]
Type 'copyright', 'credits' or 'license' for more information
IPython 9.13.0 -- An enhanced Interactive Python. Type '?' for help.
Tip: Put a ';' at the end of a line to suppress the printing of output.

In [1]: %timeit epb2jd(1957.3)
829 ns ± 1.19 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)

In [2]: %timeit zp()
421 ns ± 0.61 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)

but with this PR

In [1]: %timeit epb2jd(1957.3)
810 ns ± 1.59 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)

In [2]: %timeit zp()
418 ns ± 0.631 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)

This does not affect any wrappers that have to check the status code the ufunc returns or that take new views of any of the returned arrays.