Revert "Merge pull request #1645 from vanstee/string-split-repeats"

This reverts commit fb30101632f8e1ee94bb770ff858791aa6cba6a3, reversing
changes made to c348eb7cc58459c3ff8f117c0e7a96384ad7734b.
Accept the `trim` option when splitting strings

By default `trim` will be set to true. Because `:binary.strip` only
removes empty strings from the end of the result, we have to apply a
filter to remove empty strings from the beginning before returning.
Accept the `trim` option for `Regex.split/3`

By default `trim` will be set to true. However, since the `global` option
was implemented with the `parts` option (`{ :parts, :infinity }`), we
have to apply a filter to the final result to support `trim`.
Merge pull request #1651 from vanstee/string-split-trim

Add support for `trim` option to `String.split` and `Regex.split`