Revert "Honor $(prefix) set in config.mak* when defining ETC_GIT* and sysconfdir"

This reverts commit 2910bf56a4, as it
does not really solve the issue of making $(sysconfigdir) any more
useful than it currently is.

Makefile

@@ -291,8 +291,15 @@ sharedir = $(prefix)/share
 gitwebdir = $(sharedir)/gitweb
 template_dir = share/git-core/templates
 htmldir = share/doc/git-doc
-ETC_GITCONFIG = $(git_etcdir)/gitconfig
-ETC_GITATTRIBUTES = $(git_etcdir)/gitattributes
+ifeq ($(prefix),/usr)
+sysconfdir = /etc
+ETC_GITCONFIG = $(sysconfdir)/gitconfig
+ETC_GITATTRIBUTES = $(sysconfdir)/gitattributes
+else
+sysconfdir = $(prefix)/etc
+ETC_GITCONFIG = etc/gitconfig
+ETC_GITATTRIBUTES = etc/gitattributes
+endif
 lib = lib
 # DESTDIR=
 pathsep = :
@@ -1189,14 +1196,6 @@ endif
 -include config.mak.autogen
 -include config.mak
 
-ifeq ($(prefix),/usr)
-sysconfdir = /etc
-git_etcdir = /etc
-else
-sysconfdir = $(prefix)/etc
-git_etcdir = etc
-endif
-
 ifdef CHECK_HEADER_DEPENDENCIES
 COMPUTE_HEADER_DEPENDENCIES =
 USE_COMPUTED_HEADER_DEPENDENCIES =