Drop src_encoding.rb #2142

Job	Run time
ruby-versions / Generate Ruby versions	2s
vterm-yamatanooroti 2.7 (latest reline)	1m 22s
vterm-yamatanooroti 2.7	1m 12s
vterm-yamatanooroti 3.0 (latest reline)	29s
vterm-yamatanooroti 3.0	32s
vterm-yamatanooroti 3.1 (latest reline)	31s
vterm-yamatanooroti 3.1	33s
vterm-yamatanooroti 3.2 (latest reline)	27s
vterm-yamatanooroti 3.2	39s
vterm-yamatanooroti head (latest reline)	36s
vterm-yamatanooroti head	33s
rake test 2.7 (latest reline)	53s
rake test 2.7	40s
rake test 3.0 (latest reline)	33s
rake test 3.0	33s
rake test 3.1 (latest reline)	31s
rake test 3.1	28s
rake test 3.2 (latest reline)	32s
rake test 3.2	27s
rake test head (latest reline)	36s
rake test head	32s
rake test truffleruby-head (latest reline)	5m 29s
rake test truffleruby-head	5m 48s
	23m 58s

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