Nil elements when reslicing

[turbolent]

Description

When reslicing to pop pointer-typed elements, ensure to nil the removed elements to not leak memory.
See https://github.com/golang/go/wiki/SliceTricks#delete-without-preserving-order

---

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[github-actions]

Cadence Benchstat comparison

This branch with compared with the base branch onflow:master commit c63336c
The command for i in {1..N}; do go test ./... -run=XXX -bench=. -shuffle=on; done was used.
Bench tests were run a total of 7 times on each branch.

Results

	old.txt	new.txt
	time/op		delta
RuntimeResourceDictionaryValues-2	18.1ms ± 3%	18.4ms ± 5%	~	(p=0.259 n=7+7)
RuntimeFungibleTokenTransfer-2	1.49ms ±31%	1.54ms ±22%	~	(p=1.000 n=7+7)
ParseArray-2	16.2ms ± 5%	16.2ms ± 4%	~	(p=0.628 n=7+6)
ParseDeploy/byte_array-2	24.8ms ± 3%	24.7ms ± 6%	~	(p=0.628 n=7+6)
ParseDeploy/decode_hex-2	1.53ms ± 1%	1.53ms ± 7%	~	(p=0.731 n=6+7)
ParseInfix-2	10.6µs ± 3%	10.7µs ± 1%	~	(p=0.343 n=7+5)
ParseFungibleToken-2	245µs ± 2%	242µs ± 4%	~	(p=0.534 n=6+7)
QualifiedIdentifierCreation/One_level-2	3.48ns ± 2%	3.56ns ± 4%	~	(p=0.234 n=6+7)
QualifiedIdentifierCreation/Three_levels-2	184ns ± 4%	186ns ± 3%	~	(p=0.251 n=6+7)
CheckContractInterfaceFungibleTokenConformance-2	189µs ± 5%	183µs ± 4%	~	(p=0.053 n=7+7)
InterpretRecursionFib-2	3.46ms ± 1%	3.46ms ± 3%	~	(p=0.731 n=6+7)
NewInterpreter/new_interpreter-2	1.43µs ± 1%	1.46µs ± 8%	~	(p=0.836 n=6+7)
NewInterpreter/new_sub-interpreter-2	2.77µs ± 2%	2.82µs ± 9%	~	(p=0.945 n=6+7)
ContractInterfaceFungibleToken-2	52.8µs ± 2%	51.3µs ± 3%	−2.92%	(p=0.014 n=6+7)
	alloc/op		delta
RuntimeResourceDictionaryValues-2	4.05MB ± 0%	4.05MB ± 0%	+0.00%	(p=0.003 n=7+5)
RuntimeFungibleTokenTransfer-2	273kB ± 0%	273kB ± 0%	~	(p=0.445 n=7+6)
QualifiedIdentifierCreation/One_level-2	0.00B	0.00B	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	64.0B ± 0%	64.0B ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	26.6kB ± 0%	26.6kB ± 0%	~	(p=0.462 n=7+7)
CheckContractInterfaceFungibleTokenConformance-2	66.2kB ± 0%	66.2kB ± 0%	~	(p=1.000 n=7+7)
InterpretRecursionFib-2	1.26MB ± 0%	1.26MB ± 0%	~	(p=1.000 n=7+7)
NewInterpreter/new_interpreter-2	848B ± 0%	848B ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	1.34kB ± 0%	1.34kB ± 0%	~	(all equal)
	allocs/op		delta
RuntimeResourceDictionaryValues-2	102k ± 0%	102k ± 0%	~	(p=0.147 n=7+6)
RuntimeFungibleTokenTransfer-2	4.54k ± 0%	4.54k ± 0%	~	(p=0.755 n=7+7)
QualifiedIdentifierCreation/One_level-2	0.00	0.00	~	(all equal)
QualifiedIdentifierCreation/Three_levels-2	2.00 ± 0%	2.00 ± 0%	~	(all equal)
ContractInterfaceFungibleToken-2	458 ± 0%	458 ± 0%	~	(all equal)
CheckContractInterfaceFungibleTokenConformance-2	1.07k ± 0%	1.07k ± 0%	~	(all equal)
InterpretRecursionFib-2	26.2k ± 0%	26.2k ± 0%	~	(all equal)
NewInterpreter/new_interpreter-2	13.0 ± 0%	13.0 ± 0%	~	(all equal)
NewInterpreter/new_sub-interpreter-2	40.0 ± 0%	40.0 ± 0%	~	(all equal)