Remove tests, fuzzers and github

Merge pull request libgit2#6817 from libgit2/ethomson/v1.8.1

libgit2 v1.8.1

Merge pull request libgit2#6767 from libgit2/ethomson/v18

Release v1.8

v1.7.2: update version numbers

v1.6.5: update version numbers

fix a bug in the invokation of qsort_s

Reported in romkatv/gitstatus#414

Merge pull request libgit2#6622 from libgit2/ethomson/v1.7.1

libgit2 v1.7.1

Merge pull request libgit2#6594 from libgit2/ethomson/v1.7

v1.7: release Kleine Raupe Nimmersatt

Merge pull request libgit2#6548 from libgit2/ethomson/v1.6.4

v1.6.4 with a fix for ProgramData configs on Windows

Merge pull request libgit2#6534 from libgit2/ethomson/v1.6.3

v1.6.3