BigQuery: Parse optional DELETE FROM statement

[iffyio]

The FROM keyword is optional is a DELETE statement for BigQuery This adds parser support to handle such statements

[coveralls]

Pull Request Test Coverage Report for Build 7731356195

• -4 of 61 (93.44%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.008%) to 87.666%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tests/sqlparser_common.rs	14	15	93.33%
tests/sqlparser_bigquery.rs	14	17	82.35%

Files with Coverage Reduction	New Missed Lines	%
tests/sqlparser_common.rs	2	97.08%

Totals
Change from base Build 7660582105:	0.008%
Covered Lines:	19525
Relevant Lines:	22272

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💛 - Coveralls

[alamb]

Looks good to me -- thank you @iffyio

[iffyio]

Thanks!