dev-install: drop gmerge special casing

Now that build_image installs all the necessary files into the rootfs,
the gmerge package doesn't install anything extra.  That means we no
longer need to hardcode its install.

BUG=chromium:194889
TEST=precq passes
CQ-DEPEND=CL:1492655, CL:1497663

Change-Id: I50c7e874a270e616f7e59971f4d00ccce3c25152
Reviewed-on: https://chromium-review.googlesource.com/1497669
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/dev-install/dev_install b/dev-install/dev_install
index 21a6e41..912eec2 100755
--- a/dev-install/dev_install
+++ b/dev-install/dev_install
@@ -165,11 +165,6 @@
 }
 
 install_optional_packages() {
-  # Install gmerge manually first (even though it's part of the default
-  # virtual/target-os-dev) since it provides its own list of package.provided
-  # files.  Other packages that virtual/target-os-dev pulls in might rely on
-  # those lists, so we need them sooner rather than later.
-  emerge gmerge
   if yes_or_no "Install virtual/target-os-dev package now"; then
     emerge virtual/target-os-dev
   else