Deprecate plugins directory and sql.go file (#215)

* DummySegment and DummySubSegment creation

* Revert "DummySegment and DummySubSegment creation"

This reverts commit 4edb4b5.

* Revert "Revert "DummySegment and DummySubSegment creation""

This reverts commit 0442d84.

* ran gofmt command to remove golint warnings

* remove redundent declaration

* Added Dummysegment creation logic

* Added reviewdog suggestions

* modified code based on feedback

* even with master

* removed plugins directory and sql.go file

* Add README changes

* description change

* minor typo

README.md

@@ -118,7 +118,7 @@ Note that the `xray.Config{}` fields `LogLevel` and `LogFormat` are deprecated s
 
 ***Plugins***
 
-The plugins under "github.com/aws/aws-xray-sdk-go/plugins/" are activated at package load time. This can be convenient in some cases, but often you want to load them conditionally at runtime (e.g. don't load in tests). For this purpose, there is a new set of plugins under "github.com/aws/aws-xray-sdk-go/awsplugins/" that have an explicit `Init()` function you must call to load the plugin:
+Plugins can be loaded conditionally at runtime. For this purpose, plugins under "github.com/aws/aws-xray-sdk-go/awsplugins/" have an explicit `Init()` function. Customer must call this method to load the plugin:
 
 ```go
 import (
@@ -226,9 +226,6 @@ func main() {
   row, err := db.QueryRowContext(ctx, "SELECT 1") // Use as normal
 }
 ```
-
-Note that the `xray.SQL` are deprecated and will be remove when the SDK becomes GA.
-
 **Lambda**
 
 ```