guix: remove GCC 10 workaround from NSIS

Fixed upstream in 3.06, see
https://github.com/kichik/nsis/commit/229b6136c41ba5caba25936f4927476d20aa283f.
https://sourceforge.net/p/nsis/bugs/1248/

contrib/guix/patches/nsis-gcc-10-memmove.patch

@@ -1,23 +0,0 @@
-commit f6df41524e703dc471e283e566a48e05a735b7f2
-Author: Anders <anders_k@users.sourceforge.net>
-Date:   Sat Jun 27 23:18:45 2020 +0000
-
-    Don't let GCC 10 generate memmove calls (bug #1248)
-    
-    git-svn-id: https://svn.code.sf.net/p/nsis/code/NSIS/trunk@7189 212acab6-be3b-0410-9dea-997c60f758d6
-
-diff --git a/SCons/Config/gnu b/SCons/Config/gnu
-index bfcb362d..21fa446b 100644
---- a/SCons/Config/gnu
-+++ b/SCons/Config/gnu
-@@ -103,6 +103,10 @@ stub_env.Append(LINKFLAGS = ['$NODEFLIBS_FLAG'])    # no standard libraries
- stub_env.Append(LINKFLAGS = ['$ALIGN_FLAG'])        # 512 bytes align
- stub_env.Append(LINKFLAGS = ['$MAP_FLAG'])          # generate map file
- 
-+conf = FlagsConfigure(stub_env)
-+conf.CheckCompileFlag('-fno-tree-loop-distribute-patterns')  # GCC 10: Don't generate msvcrt!memmove calls (bug #1248)
-+conf.Finish()
-+
- stub_uenv = stub_env.Clone()
- stub_uenv.Append(CPPDEFINES = ['_UNICODE', 'UNICODE'])
-