Incorrect deletion of snippet linked placeholders

Describe the bug
When a snippet has the same placeholder twice (e.g., two instances of ${1:tag}), after expanding the snippet and pressing the backspace/delete key, everything from the beginning of the first placeholder to the end of that line is deleted, and the second placeholder is unaffected.

To Reproduce
Create the following snippet for LaTeX:

"Create environment": {
	"prefix": "begin",
	"body": [
		"\\begin{${1:env}}\n\t$0\n\\end{${1:env}}"
	],
	"description": "Create a new environment"
}

Expand this snippet, then press the delete key. The result is the following (caret represents cursor positions):

\begin{|
    
\end{env|}

Expected behavior
Both ${1:env} placeholders are deleted, resulting in the following:

\begin{|}
	
\end{|}

Environment (please complete the following information):

• Extension (VsCodeVim) version: 0.16.0
• VSCode version: 1.25.1
• OS: macOS Mojave Beta

Additional context

• LaTeX-Workshop version: 5.7.0

Start by reproducing the issue with the LaTeX snippet containing two ${1:env} placeholders in VSCodeVim 0.16.0, then trace the extension's snippet placeholder deletion handling. Done means pressing delete removes both linked placeholders while preserving the surrounding LaTeX structure and caret positions.