Updates OWNERS file

gsi_keys.mk has been removed on commit
I3714de75b94be43a1364b89b92d893b336aa014b. Removing it from
the OWNERS file and adds developer_gsi_keys.mk.

Bug: 176869478
Test: presubmit
Change-Id: I2eeee65a244c4987f217f004ec47a0b6dca9b564
diff --git a/target/product/OWNERS b/target/product/OWNERS
index 82e6e88..b3d8998 100644
--- a/target/product/OWNERS
+++ b/target/product/OWNERS
@@ -2,4 +2,4 @@
 
 # GSI
 per-file gsi_release.mk = file:/target/product/gsi/OWNERS
-per-file gsi_keys.mk = file:/target/product/gsi/OWNERS
+per-file developer_gsi_keys.mk = file:/target/product/gsi/OWNERS