Update to sagemath 8.3 (bz 1612867).

Also:
- Drop -lrslib, -gap-hap, and -flask patches.
- Drop obsolete scriplets to fix F24 to F25 upgrade (bz 1594429 and 1618934).
- Drop obsolete mktexlsr invocations.
- Fix more Singular paths.
- Fix still more uses of /usr/bin/env.
- Drop disallow/dissallow fixup for cython; now fixed in cython itself.

sagemath-fes.patch

@@ -1,7 +1,7 @@
 diff -up src/module_list.py.orig src/module_list.py
---- src/module_list.py.orig	2018-05-18 09:34:28.942183178 -0600
-+++ src/module_list.py	2018-05-18 09:35:15.210542150 -0600
-@@ -464,10 +464,10 @@ ext_modules = [
+--- src/module_list.py.orig	2018-08-29 08:35:19.927079956 -0600
++++ src/module_list.py	2018-08-29 10:41:05.127643255 -0600
+@@ -471,10 +471,10 @@ ext_modules = [
      Extension('sage.libs.ecl',
                sources = ["sage/libs/ecl.pyx"]),