examples: Remove instances of 'libc = "glibc"', simplify musl variants

Probably can remove for darwin/libSystem as well but not doing so
yet since I haven't tested anything there personally.

lib/systems/examples.nix

@@ -13,7 +13,6 @@ rec {
     config = "armv5tel-unknown-linux-gnueabi";
     arch = "armv5tel";
     float = "soft";
-    libc = "glibc";
     platform = platforms.sheevaplug;
   };
 
@@ -22,7 +21,6 @@ rec {
     arch = "armv6l";
     float = "hard";
     fpu = "vfp";
-    libc = "glibc";
     platform = platforms.raspberrypi;
   };
 
@@ -31,14 +29,12 @@ rec {
     arch = "armv7-a";
     float = "hard";
     fpu = "vfpv3-d16";
-    libc = "glibc";
     platform = platforms.armv7l-hf-multiplatform;
   };
 
   aarch64-multiplatform = rec {
     config = "aarch64-unknown-linux-gnu";
     arch = "aarch64";
-    libc = "glibc";
     platform = platforms.aarch64-multiplatform;
   };
 
@@ -51,23 +47,21 @@ rec {
     arch = "armv5tel";
     config = "armv5tel-unknown-linux-gnueabi";
     float = "soft";
-    libc = "glibc";
     platform = platforms.pogoplug4;
   };
 
   fuloongminipc = rec {
     config = "mips64el-unknown-linux-gnu";
     arch = "mips";
     float = "hard";
-    libc = "glibc";
     platform = platforms.fuloong2f_n32;
   };
 
-  muslpi = (removeAttrs raspberryPi [ "libc" ]) // {
+  muslpi = raspberryPi // {
     config = "armv6l-unknown-linux-musleabihf";
   };
 
-  aarch64-multiplatform-musl = (removeAttrs aarch64-multiplatform [ "libc" ]) // {
+  aarch64-multiplatform-musl = aarch64-multiplatform {
     config = "aarch64-unknown-linux-musl";
   };