Remove findSubstring and findSubstrings

[bgamari]

These were deprecated in 2008 (a65029c)
in favor of breakSubstring and findSubstrings appears to be incorrect
(see #180).

[bgamari]

I recommend that we release #179 as-is for 8.8.1 to avoid a major version bump which would delay the release even further. We can then release this in a subsequent major bump.

[hvr]

@bgamari I'm very reluctant to perform a major version bump (especially for a library such as bytestring which is depended upon by everyone) for the mere purpose of removing deprecated functions which pose no harm whatsoever

or put differently, I'd rather collect all low-priority API removals unti the point where something else forces a major version bump, and then execute the deprecation-removals at once.

[vdukhovni]

I fixed the findSubstrings tests in #204 . It is was merely an issue with 8-bit truncation of unicode strings introducing more matching substrings.

[vdukhovni]

I fixed the findSubstrings tests in #204 . It is was merely an issue with 8-bit truncation of unicode strings introducing more matching substrings.

With #204 merged, this PR is no longer a blocker for resolving CI issues. It might still be appropriate to merge it at some future date, but is now less pressing.
@cartazio

[Bodigrim]

This is good to go as a part of 0.11.0.0 release.