[mlir][xls] Merge assembly_format.cc/h into xls_ops.cc/h

A subsequent CL will introduce a new attribute which requires custom printing/parsing
and the separation of these libraries makes this very hard.

PiperOrigin-RevId: 812765847

Author: James Molloy

xls/contrib/mlir/BUILD

@@ -136,18 +136,6 @@ gentbl_cc_library(
     deps = [":xls_ops_td_files"],
 )
 
-cc_library(
-    name = "assembly_format",
-    srcs = ["IR/assembly_format.cc"],
-    hdrs = ["IR/assembly_format.h"],
-    deps = [
-        ":xls_ops_typedefs_inc_gen",
-        "@llvm-project//llvm:Support",
-        "@llvm-project//mlir:IR",
-        "@llvm-project//mlir:Support",
-    ],
-)
-
 cc_library(
     name = "mlir_xls",
     srcs = [
@@ -167,7 +155,6 @@ cc_library(
         "IR/xls_ops.h",
     ],
     deps = [
-        ":assembly_format",
         "@llvm-project//llvm:Support",
         "@llvm-project//mlir:FuncDialect",
         "@llvm-project//mlir:IR",