MEDIUM: proxy: remove start_proxies()

Its sole remaining purpose was to display "proxy foo started", which
has little benefit and pollutes output for those with plenty of proxies.
Let's remove it now.

The VTCs were updated to reflect this, because many of them had explicit
counts of dropped lines to match this message.

This is tagged as MEDIUM because some users may be surprized by the
loss of this quite old message.

reg-tests/lua/bad_http_clt_req_duration.vtc

@@ -26,12 +26,6 @@ varnishtest "LUA bug"
 feature ignore_unknown_macro
 
 syslog Slog {
-    recv notice
-    expect ~ "[^:\\[ ]*\\[[0-9]*\\]: Proxy f1 started"
-
-    recv notice
-    expect ~ "[^:\\[ ]\\[[0-9]*\\]: Proxy f2 started"
-
     recv info
     expect ~ "[^:\\[ ]\\[[0-9]*\\]: Ta=[0-9]* Tc=[0-9]* Td=[0-9]* Th=[0-9]* Ti=[0-9]* Tq=[0-9]* TR=[0-9]* Tr=[0-9]* Tt=[0-9]* Tw=[0-9]*$"