Remove PLATFORM_VERSION_FUTURE_CODENAMES

It has been wrong to split ALL_VERSIONS into exclusive two sets of
before/after TARGET_PLATFORM_VERSION.

And PLATFORM_VERSION_ALL_CODENAMES supports all *active* list of
non-finalized codenames.

Bug: 152960049
Test: m
Exempt-From-Owner-Approval: cp from master
Merged-In: I78ca88758998e440bea72ba2d56d90eea3ec99ae
Change-Id: I78ca88758998e440bea72ba2d56d90eea3ec99ae
(cherry picked from commit 424175d72a)

android/api_levels.go

@@ -73,7 +73,7 @@ func getApiLevelsMap(config Config) map[string]int {
 			"P":     28,
 			"Q":     29,
 		}
-		for i, codename := range config.PlatformVersionCombinedCodenames() {
+		for i, codename := range config.PlatformVersionActiveCodenames() {
 			apiLevelsMap[codename] = baseApiLevel + i
 		}