Delete unused method SourceFile.fromReader
Delete unused method SourceFile.fromReader

#codehealth

PiperOrigin-RevId: 378977049

monetate/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,google/closure-compiler,monetate/closure-compiler,google/closure-compiler,google/closure-compiler,nawawi/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,ChadKillingsworth/closure-compiler,monetate/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,monetate/closure-compiler,nawawi/closure-compiler