[roll] Roll fuchsia [build] Remove extra quotes from ln command

Building on host arm64 linux results in this error when copying fastboot:

```
[173/61923](224) COPY /usr/bin/fastboot host_arm64/fastboot
FAILED: host_arm64/fastboot
../../build/toolchain/copy_command.sh /usr/bin/fastboot host_arm64/fastboot
realpath: missing operand
Try 'realpath --help' for more information.
ln: failed to create symbolic link 'host_arm64/fastboot' -> '': No such file or directory
```

This is because this realpath invocation:

```
"$(realpath --relative-to=$(dirname "${DESTINATION}")" "$(realpath "${SOURCE}"))"
```

is interpretted as:

```
realpath '--relative-to=host_arm64 /usr/lib/android-sdk/platform-tools/fastboot'
```

I'm only able to reproduce this on linux arm64 where the shell I'm using is:

```
GNU bash, version 4.4.20(1)-release (aarch64-unknown-linux-gnu)
Copyright (C) 2016 Free Software Foundation, Inc.
```

but the shell on my x86_64 cloudtop is a much newer version, so this could be some
issue with not using ab up-to-date shell. Regardless, it looks like the intention is
that the outer double quotes shoud encompass the whole realpath invocation, but the way
it's written now instead looks like it's treated as:

```
"$(realpath --relative-to=$(dirname "${DESTINATION}")"
"$(realpath "${SOURCE}"))"
```

Original-Bug: 62896
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/778772
Original-Revision: 3348e3abbee266fd6646b1fdfcd3178e92e7e7ca
GitOrigin-RevId: 459a0ac3b1b3a371e3c787de13354cd58e21d8d6
Change-Id: I10c13367bc7ada147aff7b77af8ffab9b610a4b4