Clean up unused flags for LLD.

Since Android only uses LLD, we shouldn't be default adding flags that
just get stripped by a later pass such as:

-Wl,-m,aarch64_elf64_le_vec
-fuse-ld=gold

Remaining query for `-fuse-ld=gold`:
https://source.corp.google.com/search?q=%5C-fuse-ld%3Dgold%20file:.*%5C.(bp%7Cmk%7Cgo)&sq=package:%5Eandroid$
Remaining query for `elf64_le_vec`:
https://source.corp.google.com/search?q=elf64_le_vec%20file:.*%5C.(bp%7Cmk%7Cgo)&sq=package:%5Eandroid$

Bug: http://b/148819762
Test: Built aosp_blueline
Change-Id: I4e064a1e3e0c54721f3f08af8d717f28f6d348f8

cc/config/clang.go

@@ -80,10 +80,8 @@ var ClangUnknownCflags = sorted([]string{
 
 // Ldflags that should be filtered out when linking with clang lld
 var ClangUnknownLldflags = sorted([]string{
-	"-fuse-ld=gold",
 	"-Wl,--fix-cortex-a8",
 	"-Wl,--no-fix-cortex-a8",
-	"-Wl,-m,aarch64_elf64_le_vec",
 })
 
 var ClangLibToolingUnknownCflags = sorted([]string{})