Loose inactive samplers are already removed in
RemoveInactiveInterfaceVariables.  In-struct samplers are always marked
active by CollectVariables if the uniform is active.  If the uniform is
inactive, it is removed entirely by the translator.  Thus no inactive
samplers are left for glslang wrapper to clean up.

Bug: angleproject:3394
Change-Id: Ic0fef052afa992bd612fd22ffa1e5b9aa72a17bc
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1999488
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>