Move link_goto_model to read_goto_binary.cpp

This is the only code that uses the functions from
link_goto_model.{h,cpp}, and those functions weren't an easily usable
API anyway as a certain protocol needs to be followed.

Author: tautschnig

src/goto-programs/Makefile

@@ -28,7 +28,6 @@ SRC = adjust_float_expressions.cpp \
       json_expr.cpp \
       json_goto_trace.cpp \
       lazy_goto_model.cpp \
-      link_goto_model.cpp \
       link_to_library.cpp \
       loop_ids.cpp \
       mm_io.cpp \

src/goto-programs/README.md

@@ -567,15 +567,6 @@ deserialises the passed file into a temporary `::goto_modelt` instance, and
 then it performs 'linking' of the temporary into a passed destination
 `::goto_modelt` instance.
 
-Details about linking of `::goto_modelt` instances can be found
-[here](\ref section-linking-goto-models).
-
-\section section-linking-goto-models Linking Goto Models
-
-C++ modules:
-  - `link_goto_model.h`
-  - `link_goto_model.cpp`
-
 Dependencies:
   - [linking folder](\ref linking).
   - [typecheck](\ref section-goto-typecheck).