Revert of Adding SwiftShader compilation to Linux (patchset #1 id:1 of https://codereview.chromium.org/2528483002/ )

Reason for revert:
broke ClangToTLinuxUBSanVptr bot

Original issue's description:
> Adding SwiftShader compilation to Linux
>
> [email protected]
> BUG=630728
>
> Committed: https://crrev.com/265c779f246369ee005a817f201907a16c25290a
> Cr-Commit-Position: refs/heads/master@{#434179}

[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=630728

Review-Url: https://codereview.chromium.org/2526043003
Cr-Commit-Position: refs/heads/master@{#434264}
diff --git a/BUILD.gn b/BUILD.gn
index efd8a295..b453d53f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -525,7 +525,7 @@
     ]
   }
 
-  if (is_win || is_mac || is_linux) {
+  if (is_win || is_mac) {
     deps += [ "//third_party/swiftshader" ]
   }