refactor(tar): remove duplicate declarations

Author: akinomyoga

completions/tar

@@ -523,8 +523,7 @@ _comp_cmd_tar__detect_ext()
 
 _comp_cmd_tar__gnu()
 {
-    local basic_tar="" \
-        tar_mode tar_mode_arg
+    local basic_tar=""
 
     # Main mode, e.g. "x" or "c" or the long forms "extract" or "create"
     local tar_mode=none
@@ -710,8 +709,7 @@ _comp_cmd_tar__posix_prev_handle()
 
 _comp_cmd_tar__posix()
 {
-    local basic_tar=set \
-        tar_mode tar_mode_arg
+    local basic_tar=set
 
     # Main mode, e.g. -x or -c (extract/creation)
     local tar_mode=none