revert(3p/git): Revert merge of git upstream at v2.26.2

This causes cgit to serve error pages, which is undesirable.

This reverts commit 5229c9b232, reversing
changes made to f2b211131f.

third_party/git/.gitignore

@@ -158,7 +158,6 @@
 /git-show-branch
 /git-show-index
 /git-show-ref
-/git-sparse-checkout
 /git-stage
 /git-stash
 /git-status
@@ -217,7 +216,6 @@
 /tags
 /TAGS
 /cscope*
-*.hcc
 *.obj
 *.lib
 *.res
@@ -233,6 +231,7 @@
 *.ipdb
 *.dll
 .vs/
+*.manifest
 Debug/
 Release/
 /UpgradeLog*.htm