gnu: libgit2: Update to 0.99.0.

gnu: libgit2: Update to 0.99.0.

* gnu/packages/patches/libgit2-avoid-python.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/version-control.scm (libgit2): Update to 0.99.0.
[source](patches): Remove 'libgit2-avoid-python.patch'.
[source](snippet): Preserve bundled copy of http-parser.
[arguments]: Remove "-DUSE_SHA1DC" from #:configure-flags, which is no longer
optional and enabled by default.  Add "-DUSE_NTLMCLIENT=OFF" and
"-DREGEX_BACKEND=pcre2".  Add phase 'fix-pcre2-reference'.
[inputs]: Remove HTTP-PARSER.
[propagated-inputs]: Add PCRE2.
[native-inputs]: Remove GUILE-2.2.  Add PYTHON.