Do not export array of kmod extensions

The only user outside of libkmod-util is depmod, which really only needs
to get the string for the extension of uncompressed modules. It doesn't
need to access the array itself.
diff --git a/tools/depmod.c b/tools/depmod.c
index 74bc41f..ed1880f 100644
--- a/tools/depmod.c
+++ b/tools/depmod.c
@@ -1083,7 +1083,7 @@
 
 	if (mod->relpath != NULL) {
 		size_t uncrelpathlen = lastslash - mod->relpath + modnamesz
-				       + kmod_exts[KMOD_EXT_UNC].len;
+				       + strlen(KMOD_EXTENSION_UNCOMPRESSED);
 		mod->uncrelpath = memdup(mod->relpath, uncrelpathlen + 1);
 		mod->uncrelpath[uncrelpathlen] = '\0';
 		err = hash_add_unique(depmod->modules_by_uncrelpath,