Remove unnecessary Xcode files from package

See https://github.com/facebook/react-native/blob/v0.62.2/template/_gitignore#L5-L22.

Author: sonicdoe

ios/.npmignore

@@ -0,0 +1,16 @@
+build/
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata
+*.xccheckout
+*.moved-aside
+DerivedData
+*.hmap
+*.ipa
+*.xcuserstate