sql: make spaces without PK illegal in queries

Our SQL codebase was inherited from SQLite, where each table must have
at least one index - primary (if no explicit PK declared, one based on
rowid is implicitly created). In Tarantool spaces can exists without
indexes. The only existing restriction is that they can't contain any
data. Hence, even very basic queries fail with assertion/seagfault if
they are applied to spaces with no indexes. Situation when space turns
out to remain without PK is quite common due to the absence of
transactional DDL: for instance, space drop procedure consists of
several steps including dropping all indexes; space itself is dropped at
the very end. Thus, if a sequence of queries is interrupted by drop
space procedure and one is not finished, the rest of queries will
operate on space with no indexes.

As a solution to this problem (at least temporary) now we disallow
query processing involving spaces without PK except for views.

Closes #3780