DevTools: do not cap width of user agent override

Screenshot: https://imgur.com/a/8u2tq05

Bug: 845449
Change-Id: Ibe8ca7b40133891cfe2701f90d26a2850b7d7497
Reviewed-on: https://chromium-review.googlesource.com/1077101Reviewed-by: Andrey Lushnikov <lushnikov@chromium.org>
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577414}

third_party/blink/renderer/devtools/front_end/network/networkConfigView.css

@@ -64,7 +64,6 @@
 .network-config-ua input:not(.dt-radio-button) {
     display: block;
     width: calc(100% - 20px);
-    max-width: 250px;
 }
 
 .network-config-ua input[readonly] {