Switch to benchmark remove* instead of drop*

[natecook1000]

I added a benchmark in #32473 that was meant to help test performance of removeFirst and removeLast, but used dropFirst and dropLast instead. This rectifies that mistake!

[natecook1000]

@swift-ci Please smoke benchmark

[swift-ci]

Performance: -O

Added	MIN	MAX	MEAN	MAX_RSS
SubstringRemoveFirst1	102	108	105	—
SubstringRemoveLast1	105	105	105	—
Removed	MIN	MAX	MEAN	MAX_RSS
SubstringDropFirst1	30	30	30	—
SubstringDropLast1	24	26	25	—

Code size: -O

Regression	OLD	NEW	DELTA	RATIO
Substring.o	17155	18531	+8.0%	0.93x

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
FlattenListLoop	924	1545	+67.2%	0.60x (?)
SubstringComparable	10	11	+10.0%	0.91x (?)
Added	MIN	MAX	MEAN	MAX_RSS
SubstringRemoveFirst1	105	110	108	—
SubstringRemoveLast1	111	116	113	—
Removed	MIN	MAX	MEAN	MAX_RSS
SubstringDropFirst1	32	32	32	—
SubstringDropLast1	26	27	26	—

Code size: -Osize

Regression	OLD	NEW	DELTA	RATIO
Substring.o	17315	18573	+7.3%	0.93x

Performance: -Onone

Improvement	OLD	NEW	DELTA	RATIO
ObjectiveCBridgeStubToNSDate2	430	390	-9.3%	1.10x (?)
Added	MIN	MAX	MEAN	MAX_RSS
SubstringRemoveFirst1	95	101	99	—
SubstringRemoveLast1	98	100	99	—
Removed	MIN	MAX	MEAN	MAX_RSS
SubstringDropFirst1	145	149	147	—
SubstringDropLast1	140	143	141	—

Code size: -swiftlibs

✅	Benchmark Check Report

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac mini
  Model Identifier: Macmini8,1
  Processor Name: 6-Core Intel Core i7
  Processor Speed: 3.2 GHz
  Number of Processors: 1
  Total Number of Cores: 6
  L2 Cache (per Core): 256 KB
  L3 Cache: 12 MB
  Memory: 64 GB

[natecook1000]

@swift-ci Please smoke test and merge