Revert "Already git 2.32 is expected in doc/contributing/building_ruby.md"

This reverts commit fbc7e93.

Failures with "GCC 8" and "clang 12".
```
/github/workspace/src/tool/lib/vcs.rb:57:in `system': Command failed with status (pid 7385 exit 128): ["git", "config", "--global", "--add", "safe.directory", "/github/workspace/src"] (RuntimeError)```

Author: nobu

configure.ac

@@ -113,9 +113,10 @@ AC_ARG_WITH(git,
 {
     test x"$HAVE_GIT" = xyes &&
     command -v "$GIT" > /dev/null &&
-    # see Dependencies in doc/contributing/building_ruby.md
+    # `git -C`: 1.8.5
+    # `git log --no-show-signature`: 2.10.0
     AS_CASE([`$GIT -C . --version 2> /dev/null | sed 's/.* //'`],
-    [0.*|1.*|2.@<:@0-9@:>@.*|2.@<:@12@:>@@<:@0-9@:>@.*|2.3@<:@01@:>@.*], [false],
+    [0.*|1.*|2.@<:@0-9@:>@.*], [false],
     [true])
 } || HAVE_GIT=no GIT=never-use
 AC_SUBST(GIT)

win32/Makefile.sub

@@ -526,7 +526,7 @@ HAVE_GIT = no
 !else if [for /f "tokens=3" %I in ('git --version') do @(\
 	for /f "delims=. tokens=1-2" %I in ("%I") do @(\
 	  if %I lss 2 (exit 1) else if %I gtr 2 (exit 0) \
-	  else if %J lss 32 (exit 1) else (exit 0)\
+	  else if %J lss 10 (exit 1) else (exit 0)\
 	)\
       )]
 HAVE_GIT = no