database/sql: update minor sql docs
database/sql: update minor sql docs

Replace the work "session" with "connection" in docs. Fix
The ErrConnDone documentation. Clarify what the context is used
for in StmtContext.

Change-Id: I2f07e58d0cd6321b386a73b038cf6070cb8e2572
Reviewed-on: https://go-review.googlesource.com/65732
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

codestation/go,akutz/go,CAFxX/go,cloudflare/go,josharian/go,Cofyc/go,codestation/go,polyverse-security/go,CAFxX/go,josharian/go,cloudflare/go,cloudflare/go,nawawi/go,Cofyc/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,Cofyc/go,codestation/go,polyverse-security/go,golang/go,akutz/go,Cofyc/go,josharian/go,josharian/go,josharian/go,polyverse-security/go,CAFxX/go,Cofyc/go,Cofyc/go,nawawi/go,polyverse-security/go,codestation/go,polyverse-security/go,akutz/go,akutz/go,codestation/go,golang/go,akutz/go,golang/go,akutz/go,CAFxX/go,josharian/go,golang/go,akutz/go,akutz/go,polyverse-security/go,CAFxX/go,cloudflare/go,polyverse-security/go,nawawi/go,nawawi/go,cloudflare/go,codestation/go,codestation/go,polyverse-security/go,CAFxX/go,golang/go,josharian/go,codestation/go,nawawi/go,golang/go,nawawi/go,nawawi/go,Cofyc/go,Cofyc/go,josharian/go,golang/go,cloudflare/go,christopher-henderson/Go,CAFxX/go,cloudflare/go