pkg/web: remove dependency injection (#49123)

* pkg/web: store http.Handler internally

* pkg/web: remove injection

Removes any injection code from pkg/web.

It already was no longer functional, as we already only injected into
`http.Handler`, meaning we only inject ctx.Req and ctx.Resp.

Any other types (*Context, *ReqContext) were already accessed using the
http.Request.Context.Value() method.

* *: remove type mappings

Removes any call to the previously removed TypeMapper, as those were
non-functional already.

* pkg/web: remove Context.Invoke

was no longer used outside of pkg/web and also no longer functional

pkg/services/contexthandler/contexthandler.go

@@ -95,9 +95,8 @@ func (h *ContextHandler) Middleware(mContext *web.Context) {
 		Logger:         log.New("context"),
 	}
 
-	// Inject ReqContext into a request context and replace the request instance in the macaron context
+	// Inject ReqContext into http.Request.Context
 	mContext.Req = mContext.Req.WithContext(ctxkey.Set(mContext.Req.Context(), reqContext))
-	mContext.Map(mContext.Req)
 
 	traceID := tracing.TraceIDFromContext(mContext.Req.Context(), false)
 	if traceID != "" {
@@ -153,8 +152,6 @@ func (h *ContextHandler) Middleware(mContext *web.Context) {
 			{Num: reqContext.UserId}},
 	)
 
-	mContext.Map(reqContext)
-
 	// update last seen every 5min
 	if reqContext.ShouldUpdateLastSeenAt() {
 		reqContext.Logger.Debug("Updating last user_seen_at", "user_id", reqContext.UserId)