[R-package] remove unnecessary comments

[jameslamb]

This PR proposes removing some comments in the R package that I think are unnecessary.

There are a lot of things like this in the R code:

    # return ret
    return(ret)

Comments like this don't add any understanding of the code, but they do make it slightly harder to read and possibly lead to false positives when using git grep or similar tools to search through the codebase for things.

[StrikerRUS]

@jameslamb
Could you please fix some typos from #2912 in this PR as well?

I believe it is not "loss" but "metric" or "evaluation function".

LightGBM/R-package/R/lgb.cv.R

Line 121 in d4325c5

# If loss is a single function, store it as a 1-element list

structture, higher_bettter

LightGBM/R-package/R/lgb.cv.R

Line 595 in d4325c5

# get structture (name, higher_bettter, data_name)

Same as above for loss

LightGBM/R-package/R/lgb.train.R

Line 98 in d4325c5

# If loss is a single function, store it as a 1-element list

Maybe

assign(x = ACCUMULATOR_NAME, value = 0.0, envir = .GlobalEnv)

?

LightGBM/R-package/tests/testthat/test_basic.R

Lines 15 to 16 in d4325c5

	ACCUMULATOR_NAME <- "INCREASING_METRIC_ACUMULATOR"
	assign(x = "INCREASING_METRIC_ACUMULATOR", value = 0.0, envir = .GlobalEnv)

[jameslamb]

@StrikerRUS sure, I agree with all those! Just pushed them: 727fe46

[StrikerRUS]

@jameslamb Thank you!

[StrikerRUS]

LGTM! I agree that those removed comments don't add any value. But I guess that actual approval should come from anyone who is reading/writing R code.

[github-actions]

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