proto: remove support of number field type

This patch removes support for the `number` field type.
It also renames `number_value` to `double_value`, since that value is
the value of a `double` field.

Part of tarantool/aeon#472

Author: ImeevMA

aeon_schema.proto

@@ -43,7 +43,6 @@ enum FieldType {
   FIELD_TYPE_ANY = 1;
   FIELD_TYPE_UNSIGNED = 2;
   FIELD_TYPE_STRING = 3;
-  FIELD_TYPE_NUMBER = 4;
   FIELD_TYPE_DOUBLE = 5;
   FIELD_TYPE_INTEGER = 6;
   FIELD_TYPE_BOOLEAN = 7;

aeon_value.proto

@@ -42,7 +42,7 @@ message Value {
   oneof kind {
     uint64 unsigned_value = 1;
     string string_value = 2;
-    double number_value = 3;
+    double double_value = 3;
     sint64 integer_value = 4;
     bool boolean_value = 5;
     bytes varbinary_value = 6;