Remove PathSlice

[steiler]

The cache implmentation relied on the paths being represented as strings slices in the past.
Since the cache implementation changed quite a while ago, there is no need to keep dealing with sdcpb.Path and string slice based paths an more.
Actually reling solely on sdcpb.Path provides the abiltity to always also print the xpath representation of paths at any point, which makes the logs more meanigful.

[hansthienpondt]

LGTM, tests succeeded

[codecov]

Codecov Report

❌ Patch coverage is 55.23560% with 171 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/tree/sharedEntryAttributes.go	72.27%	46 Missing and 10 partials ⚠️
...kg/datastore/target/netconf/xml2SchemapbAdapter.go	51.51%	12 Missing and 4 partials ⚠️
pkg/datastore/clients/schema/schema_index_entry.go	17.64%	14 Missing ⚠️
pkg/utils/maps.go	0.00%	13 Missing ⚠️
pkg/tree/types/update.go	23.07%	9 Missing and 1 partial ⚠️
pkg/tree/validation_entry_leafref.go	58.82%	6 Missing and 1 partial ⚠️
pkg/tree/yang-parser-adapter.go	36.36%	7 Missing ⚠️
pkg/tree/leaf_variant_slice.go	14.28%	6 Missing ⚠️
pkg/utils/leaf_convert.go	0.00%	6 Missing ⚠️
pkg/datastore/transaction_rpc.go	0.00%	4 Missing ⚠️
... and 16 more

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