chore(config): drop unused features (#19800)

* chore: drop unused and deprecated functions

- Remove isDynamicFilePath, readConfigJson, findConfigFile, configFilename, readExpRcAsync, resetCustomC

chore(config): drop unused features (#19800)

* chore: drop unused and deprecated functions

- Remove isDynamicFilePath, readConfigJson, findConfigFile, configFilename, readExpRcAsync, resetCustomConfigPaths, setCustomConfigPath, writeConfigJsonAsync, isLegacyImportsEnabled
- Remove getManagedExtensions
- Remove target option from expo/metro-config
- Remove EXPO_TARGET environment variable support

* build

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