Replace symlink references by real path and delete symlink

The common/pc/laptop/ssd folder was apparently moved a level up and was
replaced by a symlink to keep things working. We can consolidate this now.

dell/inspiron/7405/default.nix

@@ -7,7 +7,7 @@ with lib;
     ../../../common/cpu/amd
     ../../../common/gpu/amd
     ../../../common/pc/laptop
-    ../../../common/pc/laptop/ssd
+    ../../../common/pc/ssd
   ];
 
   # TSC is unstable

dell/inspiron/7460/default.nix

@@ -3,7 +3,7 @@
 {
   imports = [
     ../../../common/pc/laptop
-    ../../../common/pc/laptop/ssd
+    ../../../common/pc/ssd
     ../../../common/gpu/intel/kaby-lake
     ../../../common/gpu/nvidia/maxwell
     ../../../common/gpu/nvidia/prime.nix

dell/inspiron/7559/README.md

@@ -41,7 +41,7 @@ This configuration uses Nvidia Prime offloading, which allows use of the `nvidia
 
 #### SSD
 
-This laptop has an optional M.2 SSD slot, which isn't accounted for here. If you are using the SSD, you could look into implementing the options in [ssd](common/pc/laptop/ssd) manually. Some sources also say you should ensure your SATA Mode is set to AHCI in your BIOS for it to be detected, however I think this is a prerequisite to installing Linux on this laptop in the first place so you probably already have that set.
+This laptop has an optional M.2 SSD slot, which isn't accounted for here. If you are using the SSD, you could look into implementing the options in [ssd](common/pc/ssd) manually. Some sources also say you should ensure your SATA Mode is set to AHCI in your BIOS for it to be detected, however I think this is a prerequisite to installing Linux on this laptop in the first place so you probably already have that set.
 
 #### Subwoofer