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-rpmbuild.patch

@@ -1,6 +1,6 @@
 diff -up src/module_list.py.orig src/module_list.py
---- src/module_list.py.orig	2018-05-16 12:35:55.223524926 -0600
-+++ src/module_list.py	2018-05-16 13:13:20.467262594 -0600
+--- src/module_list.py.orig	2018-08-29 08:34:50.846439644 -0600
++++ src/module_list.py	2018-08-29 08:35:19.927079956 -0600
 @@ -3,7 +3,7 @@ from glob import glob
  from distutils.extension import Extension
  from sage.env import SAGE_LOCAL
@@ -11,8 +11,8 @@ diff -up src/module_list.py.orig src/module_list.py
  #########################################################
  ### pkg-config setup
 diff -up src/sage/misc/cython.py.orig src/sage/misc/cython.py
---- src/sage/misc/cython.py.orig	2018-05-16 13:13:20.468262581 -0600
-+++ src/sage/misc/cython.py	2018-05-16 13:16:29.207708998 -0600
+--- src/sage/misc/cython.py.orig	2018-08-03 05:10:09.000000000 -0600
++++ src/sage/misc/cython.py	2018-08-29 08:35:19.954079622 -0600
 @@ -601,7 +601,7 @@ def cython(filename, verbose=0, compile_
      ext = Extension(name,
                      sources=[pyxfile] + extra_sources,
@@ -23,8 +23,8 @@ diff -up src/sage/misc/cython.py.orig src/sage/misc/cython.py
                      language=language)
  
 diff -up src/setup.py.orig src/setup.py
---- src/setup.py.orig	2018-05-05 16:21:27.000000000 -0600
-+++ src/setup.py	2018-05-16 13:17:40.774740719 -0600
+--- src/setup.py.orig	2018-08-03 05:10:09.000000000 -0600
++++ src/setup.py	2018-08-29 08:35:19.955079610 -0600
 @@ -370,9 +370,8 @@ class sage_build_cython(Command):
              # Debugging
              gdb_debug=self.debug,
@@ -47,9 +47,9 @@ diff -up src/setup.py.orig src/setup.py
  
      def install_kernel_spec(self):
          """
-@@ -897,40 +893,6 @@ class sage_install(install):
-         from sage.repl.ipython_kernel.install import SageKernelSpec
-         SageKernelSpec.update()
+@@ -900,40 +896,6 @@ class sage_install(install):
+         # the install_data directory for installing our Jupyter files.
+         SageKernelSpec.update(prefix=self.install_data)
  
 -    def clean_stale_files(self):
 -        """