Trac #32727: complete mpir deletion

there are leftovers:
`build/pkgs/mpir/distros/void.txt`, and in the list of deps in
`build/pkgs/4ti2/spkg-configure.m4`

URL: https://trac.sagemath.org/32727
Reported by: dimpase
Ticket author(s): Dima Pasechnik
Reviewer(s): Matthias Koeppe

build/pkgs/4ti2/spkg-configure.m4

@@ -1,5 +1,5 @@
 SAGE_SPKG_CONFIGURE([4ti2], [
-    SAGE_SPKG_DEPCHECK([gmp mpir glpk zlib], [
+    SAGE_SPKG_DEPCHECK([gmp glpk zlib], [
         dnl Debian installs these programs with an executable prefix "4ti2-",
         dnl OpenSUSE uses the prefix "4ti2_".
         dnl Singular checks for unprefixed and prefixed with "4ti2-".

build/pkgs/gfortran/SPKG.rst

@@ -22,7 +22,7 @@ Dependencies
 ------------
 
 -  zlib
--  MPIR
+-  GMP 
 -  MPFR
 -  MPC
 

build/pkgs/mpc/spkg-install.in

@@ -1,7 +1,7 @@
 cd src
 
 # Unset CC and CFLAGS.  This will make mpc use the same configuration
-# as MPIR, which is probably a good thing.
+# as GMP, which is probably a good thing.
 unset CC
 unset CFLAGS