completeFunctionCalls should not add this parameters

[xuanduc987]

• VSCode Version: 1.47.3
• OS Version: Darwin x64 18.7.0

Steps to Reproduce:

1. Enable completeFunctionCall
2. Create new tyepscript file, ype

function f(this: void) {
	// make sure `this` is unusable in this standalone function
}
f|

cursor at |
3. TAB

Expected: f()
Actual: f(this)

Typescript allow annotating this parameter https://www.typescriptlang.org/docs/handbook/functions.html#this-parameters

function f(this: void) {
  // make sure `this` is unusable in this standalone function
}

Because this parameters are fake parameters, I think we should skip these.

Does this issue occur when all extensions are disabled?: Yes/No