Simplify stdlib function literals ("->", elide "return")

[tmaxmax]

found 7523 function literals, 4674 (62.1%) rewritten into lightweight form
1841 lightweight function literals (39.4%) are in test files
1946 lightweight function literals contain a single statement
        (from which 353, 18.1% are long)
721 lightweight function literals contain a single return statement
        (15.4% of all rewritten literals, 37.1% of single statement literals)
return value count histogram for single-return lightweight function literals:
        [0 638 81 2 0 0 0 0 0 0]