dslx_fmt breaks files with arrays of channels

[rw1nkler]

When a file with a Proc that contains an array of channels is passed to dslx_fmt, the tool formats it incorrectly.
As a result, the file can no longer be parsed correctly by the DSLX interpreter.

diff --git a/xls/examples/bug.x b/xls/examples/bug.x
index a36002d8b..188823d81 100644
--- a/xls/examples/bug.x
+++ b/xls/examples/bug.x
@@ -15,12 +15,12 @@ proc Passthrough {
 #[test_proc]
 proc SimpleTest {
     terminator: chan<bool> out;
-    input_s: chan<u32>[2] out;
-    output_r: chan<u32>[2] in;
+    input_s: chan<u32> out2;
+    output_r: chan<u32> in2;

     config(terminator: chan<bool> out) {
-        let (input_s, input_r) = chan<u32>[2];
-        let (output_s, output_r) = chan<u32>[2];
+        let (input_s, input_r) = chan<u32>2;
+        let (output_s, output_r) = chan<u32>2;

         spawn Passthrough(input_r[0], output_s[0]);
         spawn Passthrough(input_r[1], output_s[1]);

Here is the input file that I used: bug.x.
Tested on current main branch (8aacd820)