DOC: replace deprecated freqs in user_guide Period

[natmokval]

xref #54061

replaced deprecated frequencies in user_guide Period with new frequencies.

[phofl]

Can you grep that they aren't anywhere else?

[phofl]

thx @natmokval

[natmokval]

Can you grep that they aren't anywhere else?

yes, I used grep to check if there are anywhere else frequencies which are deprecated.
I found a couple of places where comments contain deprecated frequencies. For example in pandas/_libs/tslibs/period.pyx we have deprecated 'T': # ('T', 5) but may be passed in as a string like '5T'

I am not sure, should I change 'T' to "min' in the comment?

Also we have in asv_bench/benchmarks/ some tests with deprecated frequencies "S" and "H". I think it's better to replace them with valid frequencies, are you agree?
Could you please explain why when I run tests in asv_bench/benchmarks/ with deprecated frequencies they don't fail.

[natmokval]

thanks for reviewing this PR @phofl