gnu: Replace libgit2-1.9 with default libgit2 where possible.

* gnu/packages/guile.scm (guile-git): Replace libgit2-1.9 with libgit2
* gnu/packages/package-management.scm (nix): Replace libgit2-1.9 with libgit2
* gnu/packages/python-xyz.scm (python-pygit2-1.18): Replace libgit2-1.9 with libgit2

Change-Id: Icc77f5b4289f1805764e1b3fdd29062524c61c24
Signed-off-by: Andreas Enge <andreas@enge.fr>

gnu/packages/guile.scm

@@ -939,7 +939,7 @@ type system, elevating types to first-class status.")
     (native-inputs
      (list pkg-config autoconf automake texinfo guile-3.0 guile-bytestructures))
     (inputs
-     (list guile-3.0 libgit2-1.9))
+     (list guile-3.0 libgit2))
     (propagated-inputs
      (list guile-bytestructures))
     (synopsis "Guile bindings for libgit2")

gnu/packages/package-management.scm

@@ -977,7 +977,7 @@ by using a Xapian cache.")
                    libarchive
                    libblake3
                    libgc
-                   libgit2-1.9
+                   libgit2
                    libseccomp
                    libsodium
                    lowdown

gnu/packages/python-xyz.scm

@@ -11607,7 +11607,7 @@ readable format.")
        (uri (pypi-uri "pygit2" version))
        (sha256
         (base32 "0m8g8s72c0xwwayykpj1hf8c1wldhmg1sj8kgxdp2rf9c837xa7c"))))
-    (propagated-inputs (list python-cffi libgit2-1.9))))
+    (propagated-inputs (list python-cffi libgit2))))
 
 (define-public python-patiencediff
   (package