Changes the default values of literal on top parameters.

We confiremed that following two parameters have no positive but negative impact so
set default values (0) to turn off these features.
typing_correction_literal_on_top_conversion_cost_max_diff
typing_correction_literal_on_top_correction_score_max_diff

typing_correction_literal_at_least_second are enabled both in canary and production,
so we change the default value.

PiperOrigin-RevId: 627983164

src/data/test/session/scenario/b7321313_scenario.txt

@@ -19,8 +19,7 @@ SEND_KEY	RIGHT
 SEND_KEYS	44444111
 
 # The result should be "鉄道" for now.
-# TODO(taku): change the default param so literal-on-top stops working.
-EXPECT_CANDIDATE	1	鉄道
+EXPECT_CANDIDATE	0	鉄道
 
 # Move the caret to the beginnig, and back to the end.
 SEND_KEY	LEFT
@@ -31,5 +30,4 @@ SEND_KEY	RIGHT
 SEND_KEY	RIGHT
 
 # The candidate is still "鉄道"
-# TODO(taku): change the default param so literal-on-top stops working.
-EXPECT_CANDIDATE	1	鉄道
+EXPECT_CANDIDATE	0	鉄道

src/protocol/commands.proto

@@ -626,9 +626,9 @@ message DecoderExperimentParams {
   //   typing_correction_literal_on_top_length_score_max_diff
   //     * (typing_correction_literal_on_top_length_decay^(input_length-3))
   optional float typing_correction_literal_on_top_correction_score_max_diff = 47
-      [default = 0.5];
+      [default = 0.0];
   optional int32 typing_correction_literal_on_top_conversion_cost_max_diff = 48
-      [default = 2000];
+      [default = 0];
   // Literal candidate is placed at least second position.
   optional bool typing_correction_literal_at_least_second = 49
       [default = false];