Cleanup fast pipe implementation

esy.json

@@ -32,6 +32,7 @@
     "install": [
       ["esy-installer", "reason.install"],
       ["esy-installer", "rtop.install"]
-    ]
+    ],
+    "buildsInSource": "_build"
   }
 }

formatTest/errorTests/expected_output/reservedField.re

@@ -1,2 +1,2 @@
 File "reservedField.re", line 1, characters 11-15:
-Error: 1050: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead
+Error: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead

formatTest/errorTests/expected_output/reservedRecord.re

@@ -1,2 +1,2 @@
 File "reservedRecord.re", line 1, characters 24-28:
-Error: 1821: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead
+Error: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead

formatTest/errorTests/expected_output/reservedRecordPunned.re

@@ -1,2 +1,2 @@
 File "reservedRecordPunned.re", line 1, characters 22-26:
-Error: 3369: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead
+Error: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead

formatTest/errorTests/expected_output/reservedRecordType.re

@@ -1,2 +1,2 @@
 File "reservedRecordType.re", line 1, characters 11-15:
-Error: 766: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead
+Error: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead

formatTest/errorTests/expected_output/reservedRecordTypePunned.re

@@ -1,2 +1,2 @@
 File "reservedRecordTypePunned.re", line 1, characters 11-15:
-Error: 766: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead
+Error: type is a reserved keyword, it cannot be used as an identifier. Try `type_` or `_type` instead