BUG/MINOR: connection/debug: do not enforce !event_type on subscribe() anymore

When building with DEBUG_STRICT, there are still some BUG_ON(events&event_type)
in the subscribe() code which are not welcome anymore since we explicitly
permit to wake the caller up on readiness. This causes some regtests to fail
since 2c1f37d353 ("OPTIM: mux-h1: subscribe rather than waking up at a few
other places") when built with this option.

No backport is needed, this is 2.2-dev.
diff --git a/src/mux_fcgi.c b/src/mux_fcgi.c
index 6a7a13f..7254add 100644
--- a/src/mux_fcgi.c
+++ b/src/mux_fcgi.c
@@ -3712,7 +3712,6 @@
 	struct fcgi_conn *fconn = fstrm->fconn;
 
 	BUG_ON(event_type & ~(SUB_RETRY_SEND|SUB_RETRY_RECV));
-	BUG_ON(fstrm->subs && fstrm->subs->events & event_type);
 	BUG_ON(fstrm->subs && fstrm->subs != es);
 
 	es->events |= event_type;
diff --git a/src/mux_h1.c b/src/mux_h1.c
index a07654b..2e2dbf9 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -2587,7 +2587,6 @@
 		return -1;
 
 	BUG_ON(event_type & ~(SUB_RETRY_SEND|SUB_RETRY_RECV));
-	BUG_ON(h1s->subs && h1s->subs->events & event_type);
 	BUG_ON(h1s->subs && h1s->subs != es);
 
 	es->events |= event_type;
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 478f3c4..b872897 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -5611,7 +5611,6 @@
 	TRACE_ENTER(H2_EV_STRM_SEND|H2_EV_STRM_RECV, h2c->conn, h2s);
 
 	BUG_ON(event_type & ~(SUB_RETRY_SEND|SUB_RETRY_RECV));
-	BUG_ON(h2s->subs && h2s->subs->events & event_type);
 	BUG_ON(h2s->subs && h2s->subs != es);
 
 	es->events |= event_type;
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index efb6b0e..2688117 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -6473,7 +6473,6 @@
 		return -1;
 
 	BUG_ON(event_type & ~(SUB_RETRY_SEND|SUB_RETRY_RECV));
-	BUG_ON(ctx->subs && ctx->subs->events & event_type);
 	BUG_ON(ctx->subs && ctx->subs != es);
 
 	ctx->subs = es;
diff --git a/src/xprt_handshake.c b/src/xprt_handshake.c
index 89446af..bfbd522 100644
--- a/src/xprt_handshake.c
+++ b/src/xprt_handshake.c
@@ -203,7 +203,6 @@
 	struct xprt_handshake_ctx *ctx = xprt_ctx;
 
 	BUG_ON(event_type & ~(SUB_RETRY_SEND|SUB_RETRY_RECV));
-	BUG_ON(ctx->subs && ctx->subs->events & event_type);
 	BUG_ON(ctx->subs && ctx->subs != es);
 
 	ctx->subs = es;