Remove unnecessary completion item data field

[jdneo]

• The signature information is not needed to store in the completion item data field. It can be retrieved from the proposal that stored in the completion response cache.

fix #2645
fix #2638

Complete after a string variable. the response data can be reduced from 83.7KB to 70.4KB

[rgrunber]

Confirmed the payload reduction. A ~20% reduction in the size of a completion item that's a method/type proposal.

$ ls -sh old.txt new.txt 
68K new.txt  84K old.txt

--- old.txt 2023-05-10 14:59:50.490531788 -0400
+++ new.txt 2023-05-10 15:08:33.875918949 -0400
@@ -1,4 +1,4 @@
-[Trace - 14:59:14] Received response 'textDocument/completion - (41)' in 269ms.
+[Trace - 15:08:05] Received response 'textDocument/completion - (40)' in 339ms.
 Result: {
     "isIncomplete": false,
     "items": [
@@ -110,9 +110,6 @@
                 ]
             },
             "data": {
-                "decl_signature": "Lorg.example.Main;",
-                "signature": "(Ljava.lang.String;Ljava.lang.Class<*>;)Ljava.lang.Object;",
-                "name": "deserializeData",
                 "pid": "4",
                 "rid": "0"
             }
@@ -137,9 +134,6 @@
                 ]
             },
             "data": {
-                "decl_signature": "Lorg.example.Main;",
-                "signature": "([Ljava.lang.String;)V",
-                "name": "main",
                 "pid": "5",
                 "rid": "0"
             }
@@ -164,7 +158,6 @@
                 ]
             },
             "data": {
-                "decl_signature": "Lorg.example.Main;",
                 "pid": "6",
                 "rid": "0"
             }