Simplify thrift generator for setter methods

Summary:
To eventually get rid of usage of non-compat setter methods

#build_rule_type[go_library,go_binary]

Reviewed By: podtserkovskiy

Differential Revision: D69127191

fbshipit-source-id: a8c215e3f1cac9deef1c6d5bbd14a76856a1c03c

third-party/thrift/src/thrift/compiler/generate/templates/go/types/field_method_set.mustache

@@ -26,14 +26,6 @@ func (x *{{struct:go_name}}) {{field:go_setter_name}}{{#program:compat_setters?}
 {{#program:compat_setters?}}
 
 func (x *{{struct:go_name}}) {{field:go_setter_name}}(value {{#field:compat_setter_pointer?}}*{{/field:compat_setter_pointer?}}{{#field:type}}{{> common/type}}{{/field:type}}) *{{struct:go_name}} {
-    {{#field:compat_setter_pointer?}}
-    {{^field:pointer?}}
-    if (value == nil) {
-        x.{{field:go_name}} = nil
-        return x
-    }
-    {{/field:pointer?}}
-    {{/field:compat_setter_pointer?}}
     x.{{field:go_name}} = {{field:compat_setter_value_op}}value
     return x
 }