Remove wrapper for search_shortcuts metrics

[mcarare]

Implemented in #793.

Breakout from #21292.

┆Issue is synchronized with this Jira Task

[LaurentiuApahideanSV]

I tested the issue on Firefox Nightly 2022-04-01 by performing searches using the search shortcuts with all available search engines and custom ones and observing the events that are generated.

Selecting Google as a search engine
{
"timestamp": 9754,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "Google"
}

Selecting Amazon as a search engine
{
"timestamp": 21355,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "Amazon.com"
}

Selecting Bing as a search engine
{
"timestamp": 23735,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "Bing"
}

Selecting DuckDuckGo as a search engine
{
"timestamp": 33757,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "DuckDuckGo"
}

Selecting Wikipedia as a search engine
{
"timestamp": 61841,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "Wikipedia"
}

Selecting Google as a search engine
{
"timestamp": 74526,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "eBay"
}
Selecting Reddit as a search engine
{
"timestamp": 8757,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "Reddit"
}
Selecting a custom search engine (when using any custom search engine the engine will always be custom)
{
"timestamp": 7309,
"category": "search_shortcuts",
"name": "selected",
"extra": {
"engine": "custom"
}

When any search is performed using search engine shortcuts
{
"timestamp": 26222,
"category": "events",
"name": "performed_search",
"extra": {
"source": "shortcut.action"
}
Glean Dashboard

Device used:

• OnePlus 6T (Android 9)