remove obsolete and unused Racket-to-C compiler

Removes `raco ctool -e/-c', `mzc -e/-c', `compile-extensions',
`compile-extensions-to-c', `compile-c-extensions', `compiler/cffi',
`compiler/comp-unit', `compiler:inner^', and most options in
`compiler/option'.

original commit: 0ab6637539

collects/compiler/sig.rkt

@@ -4,8 +4,7 @@
 (require mzlib/unit)
 
 (provide compiler:option^
-         compiler^
+         compiler^)
-         compiler:inner^)
 
 ;; Compiler options
 (define-signature compiler:option^
@@ -21,61 +20,17 @@
                 ;  the public names of loaded extensions
                 ; default = ""
 
-   clean-intermediate-files ; #t => keep intermediate .c/.o files
-                            ; default = #f
-
    3m ; #t => build for 3m
       ; default = #f
 
    compile-subcollections   ; #t => compile collection subdirectories
                             ; default = #t
 
-   compile-for-embedded     ; #f => make objects to be linked
-                            ; directly with Racket, not dynamically
-                            ; loaded; default = #f
-
-   max-inline-size          ; max size of inlined procedures
-
-   disable-interrupts       ; #t => UNSAFE: turn off breaking, stack
-                            ; overflow, and thread switching;
-                            ; default = #f
-   unsafe                   ; #t => UNSAFE: omit some type checks
-                            ; default = #f
-   fixnum-arithmetic        ; #t => UNSAFE: don't check for overflow or
-                            ; underflow for fixnum arithmetic;
-                            ; default = #f
-
-   propagate-constants      ; default = #t
-   assume-primitives        ; #t => car = #%car; default = #f
-   stupid                   ; allow obvious non-syntactic errors;
-                            ;  e.g.: ((lambda () 0) 1 2 3)
-
-   vehicles                 ; Controls how closures are compiled:
-                            ;  'vehicles:automatic,
-                            ;  'vehicles:functions,
-                            ;  'vechicles:units, or
-                            ;  'vehicles:monolithic.
-                            ; default = 'vehicles:automatic
-   vehicles:monoliths       ; Size for 'vehicles:monolithic
-   seed                     ; Randomizer seed for 'vehicles:monolithic
-
-   max-exprs-per-top-level-set ; Number of top-level Scheme expressions
-                               ; crammed into one C function; default = 25
-
-   unpack-environments      ; default = #t
-   		           ; Maybe #f helps for register-poor architectures?
-
-   debug ; #t => creates debug.txt debugging file
-   test  ; #t => ignores top-level expressions with syntax errors
    ))
 
 ;; Compiler procedures
 (define-signature compiler^
-  (compile-extensions
+  (compile-zos
-   compile-extensions-to-c
-   compile-c-extensions
-
-   compile-zos
 
    compile-collection-zos
    compile-directory-zos
@@ -83,10 +38,3 @@
 
    current-compiler-dynamic-require-wrapper
    compile-notify-handler))
-
-;; Low-level extension compiler interface
-(define-signature compiler:inner^
-  (compile-extension
-   compile-extension-to-c
-   compile-c-extension
-   eval-compile-prefix))