remove redundant unsafe-addition lint setting from config

Summary:
Changelog: [Internal]

This lint is now an error by default, so we no longer need to manually specify it as such in the flowconfig. This also gets us ready to remove the lint entirely from Flow.

Reviewed By: gkz

Differential Revision: D23134689

fbshipit-source-id: 683a414bb399b823c65b7f687d25344d3e3ba980

.flowconfig

@@ -69,7 +69,6 @@ unsafe-getters-setters=warn
 unnecessary-invariant=warn
 signature-verification-failure=warn
 deprecated-utility=error
-unsafe-addition=error
 
 [strict]
 deprecated-type

.flowconfig.android

@@ -69,7 +69,6 @@ unsafe-getters-setters=warn
 unnecessary-invariant=warn
 signature-verification-failure=warn
 deprecated-utility=error
-unsafe-addition=error
 
 [strict]
 deprecated-type