Revert "add an infinity-loop detection to block-level parsing"

This reverts commit 0c62e28e900533ff5d0376fac2e5b0c4894e1fa3.

block.go

@@ -31,23 +31,8 @@ func (p *parser) block(out *bytes.Buffer, data []byte) {
 	}
 	p.nesting++
 
-	lastLen := 0
-	sameLenCount := 0
-
 	// parse out one block-level construct at a time
 	for len(data) > 0 {
-		curLen := len(data)
-		if curLen == lastLen {
-			sameLenCount += 1
-			if sameLenCount >= 3 {
-				// infinity loop detection
-				return
-			}
-		} else {
-			sameLenCount = 0
-		}
-		lastLen = curLen
-
 		// prefixed header:
 		//
 		// # Header 1