Revert "[Reland][DWARFLinkerParallel] Add limited functionality to DWARFLinkerParallel."

This reverts commit 0229dd06.

This introduces two test failures on s390x.

tools/dsymutil/X86/location-expression.test:

    warning: cann't load line table.
    note: while processing CU1
    /builddir/build/BUILD/llvm-18.0.0.src/test/tools/dsymutil/X86/location-expression.test:20:10: error: CHECK: expected string not found in input
    # CHECK: DW_AT_name{{.*}}"CU1"
             ^
    <stdin>:34:32: note: scanning from here
    0x0000000b: DW_TAG_compile_unit [1] *
                                   ^
    <stdin>:37:2: note: possible intended match here
     DW_AT_name [DW_FORM_strp] ( .debug_str[0x09000000] = )
     ^

tools/dsymutil/X86/tls-variable.test:

    warning: cann't load line table.
    note: while processing CU1
    /builddir/build/BUILD/llvm-18.0.0.src/test/tools/dsymutil/X86/tls-variable.test:19:10: error: CHECK: expected string not found in input
    # CHECK: DW_AT_name{{.*}}"CU1"
             ^
    <stdin>:26:32: note: scanning from here
    0x0000000b: DW_TAG_compile_unit
                                   ^
    <stdin>:29:2: note: possible intended match here
     DW_AT_name ()
     ^