.vscode: remove accidentally added MOCHA_GREP

By accident, committed this in go.dev/cl/411104

Change-Id: I491c384e5ed24af44faf0941beb9818ded9abe23
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/412391
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>

.vscode/launch.json

@@ -63,7 +63,6 @@
 			"env": {
 				"VSCODE_GO_IN_TEST": "1",  // Disable code that shouldn't be used in test
 				"MOCHA_TIMEOUT": "999999",
-				"MOCHA_GREP": "Error checking"
 			},
 			"stopOnEntry": false,
 			"sourceMaps": true,