Remove LcovMerger from tools/test:embedded_tools.
`CoverageOutputGenerator` is actually embedded into `bazel_tools` through [//tools:embedded_tools_srcs](https://github.com/bazelbuild/bazel/blob/master/tools/BUILD#L61).
The referenced changed in this PR is useless so I just deleted it.
Closes
@@ -121,7 +121,7 @@ filegroup(
"generate-xml.sh",
"collect_coverage.sh",
"collect_cc_coverage.sh",
- ] + glob(["LcovMerger/**"]) + select({
+ ] + select({
"@bazel_tools//src/conditions:windows": [
"tw",
"xml",
