git-svn: disable _rev_list memoization

This memoization appears unneeded as the check_cherry_pick2 cache is
in front of it does enough.

With this change applied, importing from local svn+ssh and http copies
of the R repo[1] takes only 2:00 (2 hours) on my system and the git-svn
process never uses more than 60MB RSS on my x86-64 GNU/Linux system[2].
This 60M measurement is only for the git-svn Perl process itself and
does not include memory used by git subprocesses accessing large packs
(subprocess memory usage _is_ measured by my time(1) tool).

Before this change, an import took longer (2:20) on svn+ssh:// but
git-svn used around 240MB during the imports.  Worse yet, git-svn
ballooned to over 400M when writing out the cache to the filesystem.

I also tried removing memoization for `has_no_changes', too, but a
local copy of the R repository(*) was not close to finishing within
10 hours on my system.

[1] http://svn.r-project.org/R
[2] file:// repos causes libsvn to use more memory internally

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Hin-Tak Leung <htl10@users.sourceforge.net>

perl/Git/SVN.pm

@@ -1600,7 +1600,6 @@ sub tie_for_persistent_memoization {
 		my %lookup_svn_merge_cache;
 		my %check_cherry_pick2_cache;
 		my %has_no_changes_cache;
-		my %_rev_list_cache;
 
 		tie_for_persistent_memoization(\%lookup_svn_merge_cache,
 		    "$cache_path/lookup_svn_merge");
@@ -1622,14 +1621,6 @@ sub tie_for_persistent_memoization {
 			SCALAR_CACHE => ['HASH' => \%has_no_changes_cache],
 			LIST_CACHE => 'FAULT',
 		;
-
-		tie_for_persistent_memoization(\%_rev_list_cache,
-		    "$cache_path/_rev_list");
-		memoize '_rev_list',
-			SCALAR_CACHE => 'FAULT',
-			LIST_CACHE => ['HASH' => \%_rev_list_cache],
-		;
-
 	}
 
 	sub unmemoize_svn_mergeinfo_functions {
@@ -1639,7 +1630,6 @@ sub tie_for_persistent_memoization {
 		Memoize::unmemoize 'lookup_svn_merge';
 		Memoize::unmemoize 'check_cherry_pick2';
 		Memoize::unmemoize 'has_no_changes';
-		Memoize::unmemoize '_rev_list';
 	}
 
 	sub clear_memoized_mergeinfo_caches {