Remove -Wl,--gc-sections from target flags

-Wl,--gc-sections is already added by library.go and binary.go for
anything that uses bionic.

Bug: 68855788
Test: m checkbuild
Change-Id: I229199045ef8595d69c07fcf1aa6bbdc0b753fe3

cc/config/x86_64_device.go

@@ -40,7 +40,6 @@ var (
 		"-Wl,--build-id=md5",
 		"-Wl,--warn-shared-textrel",
 		"-Wl,--fatal-warnings",
-		"-Wl,--gc-sections",
 		"-Wl,--hash-style=gnu",
 		"-Wl,--no-undefined-version",
 	}

cc/config/x86_device.go

@@ -46,7 +46,6 @@ var (
 		"-Wl,--build-id=md5",
 		"-Wl,--warn-shared-textrel",
 		"-Wl,--fatal-warnings",
-		"-Wl,--gc-sections",
 		"-Wl,--hash-style=gnu",
 		"-Wl,--no-undefined-version",
 	}

cc/config/x86_linux_bionic_host.go

@@ -55,7 +55,6 @@ var (
 		"-Wl,--build-id=md5",
 		"-Wl,--warn-shared-textrel",
 		"-Wl,--fatal-warnings",
-		"-Wl,--gc-sections",
 		"-Wl,--hash-style=gnu",
 		"-Wl,--no-undefined-version",