Zed update through "remove mapstructure" by mccanne

This is an auto-generated commit with a Zed dependency update. The Zed PR
brimdata/zed#2703, authored by @mccanne,
has been merged.

remove mapstructure

I have tripped over mapstructure one too many times so this commit
removes it.  When/if the extra round-trip through JSON adds
measurable overhead to Zed query times, we can revisit this and
hopefully mapstructure will be more mature.  For now, I wanted to
add order.Which to proc.Sort and similar but mapstructure cannot
handle custom JSON unmarshalers so this caused unpack to fail
for apparently no reason.

See mitchellh/mapstructure#115

package.json

@@ -155,7 +155,7 @@
     "styled-components": "^5.1.1",
     "tree-model": "^1.0.7",
     "valid-url": "^1.0.9",
-    "zed": "git+https://github.com/brimdata/zed.git#3dcb327e99cb2d9564af5f316fa07517fa47b5a4"
+    "zed": "git+https://github.com/brimdata/zed.git#730d19c91f99cb3747143a56c73b5c16b8ba0da6"
   },
   "optionalDependencies": {
     "electron-installer-debian": "^3.0.0",