Remove symbol-related static asserts

Remove symbol-related static asserts

commit 3573abe1d added static asserts to ensure that symbol sizes
don't vary.  However, this failed to build on Windows, on at least one
ARM platform (see PR build/25182) and internally at AdaCore for PPC.

So, I think it is probably best to just remove these assertions,
effectively reverting 3573abe1d.

gdb/ChangeLog
2019-11-13  Tom Tromey  <tromey@adacore.com>

	PR build/25182:
	* psympriv.h (partial_symbol): Remove static assert.
	* symtab.h (general_symbol_info, symbol): Remove static assert.

Change-Id: I51940fb2240c474838b48494b5072081701789bb