DOC: remove 'count_reduce_items' from the 'Counting' section.
Merge pull request #4957 from WarrenWeckesser/doc-fix

DOC: remove 'count_reduce_items' from the 'Counting' section.
Fixed two typos in the c-api user guide.
Merge pull request #4961 from cel4/tiny_doc_fixes

Fixed two typos in the c-api user guide.