Bug 1409436 - Fix jsterm font-size warning; r=Honza.

The font-size property was trying to retrieve a non existing variable, which
was spamming the terminal with warning messages. Putting the property to
inherit since it was defaulted to that.

MozReview-Commit-ID: nMWUOvOTIt

--HG--
extra : rebase_source : 35b07bccdb7fd2da89957393c01d68268e6b99fe

devtools/client/themes/webconsole.css

@@ -446,7 +446,7 @@ textarea.jsterm-complete-node {
   margin: 0;
   background-color: transparent;
   resize: none;
-  font-size: var(--theme-toolbar-font-size);
+  font-size: inherit;
   line-height: 16px;
   overflow-x: hidden;
   /* Set padding for console input on textarea to make sure it is included in