patch 8.1.2128: renamed libvterm sources makes merging difficult

Problem:    Renamed libvterm sources makes merging difficult.
Solution:   Rename back to the original name and only rename the .o files.
            Also clean the libvterm build artifacts. (James McCoy,
            closes #5027)
diff --git a/src/version.c b/src/version.c
index 06454ef..7ad0acd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -754,6 +754,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2128,
+/**/
     2127,
 /**/
     2126,