Revert part of #4225

Since in mruby, Integer and Float interchange frequently (mostly on
overflow), so adding explicit `.0` can cause problems sometimes.

For example:
https://github.com/mattn/mruby-json/pull/40
https://github.com/pepabo/mruby-msd/pull/13
https://github.com/mattn/mruby-json/pull/42

src/numeric.c

@@ -246,9 +246,6 @@ flo_to_s(mrb_state *mrb, mrb_value flt)
       str = mrb_float_to_str(mrb, flt, fmt);
       goto insert_dot_zero;
     }
-    else {
-      mrb_str_cat(mrb, str, ".0", 2);
-    }
 
     return str;
   }

test/t/float.rb

@@ -212,10 +212,10 @@ assert('Float#to_s') do
   assert_equal("Infinity", Float::INFINITY.to_s)
   assert_equal("-Infinity", (-Float::INFINITY).to_s)
   assert_equal("NaN", Float::NAN.to_s)
-  assert_equal("0.0", 0.0.to_s)
-  assert_equal("-0.0", -0.0.to_s)
+  assert_equal("0", 0.0.to_s)
+  assert_equal("-0", -0.0.to_s)
   assert_equal("-3.25", -3.25.to_s)
-  assert_equal("50.0", 50.0.to_s)
+  assert_equal("50", 50.0.to_s)
   assert_equal("0.0125", 0.0125.to_s)
   assert_equal("-0.0125", -0.0125.to_s)
   assert_equal("1.0e-10", 0.0000000001.to_s)
@@ -224,8 +224,8 @@ assert('Float#to_s') do
   assert_equal("-1.0e+20", -1e20.to_s)
   assert_equal("1.0e+16", 10000000000000000.0.to_s)
   assert_equal("-1.0e+16", -10000000000000000.0.to_s)
-  assert_equal("100000.0", 100000.0.to_s)
-  assert_equal("-100000.0", -100000.0.to_s)
+  assert_equal("100000", 100000.0.to_s)
+  assert_equal("-100000", -100000.0.to_s)
   if uses_float
     assert_equal("1.0e+08", 100000000.0.to_s)
     assert_equal("-1.0e+08", -100000000.0.to_s)
@@ -234,8 +234,8 @@ assert('Float#to_s') do
   else
     assert_equal("1.0e+15", 1000000000000000.0.to_s)
     assert_equal("-1.0e+15", -1000000000000000.0.to_s)
-    assert_equal("100000000000000.0", 100000000000000.0.to_s)
-    assert_equal("-100000000000000.0", -100000000000000.0.to_s)
+    assert_equal("100000000000000", 100000000000000.0.to_s)
+    assert_equal("-100000000000000", -100000000000000.0.to_s)
   end
 end