gnu: Remove 'gcc-glibc-2.27' and 'gcc-glibc-2.26'.

These top-level references to GCC could cause problems, such as:

  $ guix build -e '(@ (gnu packages gcc) gcc)' -n
  guix build: error: failed to evaluate expression '(@ (gnu packages gcc) gcc)':
  In procedure module-lookup: Unbound variable: gcc

Regression introduced in 3ed497d42a.

* gnu/packages/base.scm (gcc-glibc-2.27, gcc-glibc-2.26): Remove.

gnu/packages/base.scm

@@ -1032,12 +1032,6 @@ with the Linux kernel.")
                         (fold alist-delete (%final-inputs) '("libc" "libc:static")))))
            (inputs '())))
 
-(define-public gcc-glibc-2.27
-  (make-gcc-libc gcc glibc-2.27))
-
-(define-public gcc-glibc-2.26
-  (make-gcc-libc gcc glibc-2.26))
-
 (define-public (make-glibc-locales glibc)
   (package
     (inherit glibc)