meta: remove call to _meta_in_progress(), fix multisample enable/disable

meta: remove call to _meta_in_progress(), fix multisample enable/disable

This partially reverts d638da23d2ec2e9c52655b1ea138249e7f8bcccb.

With gallium the meta code is not always built so the call to
_meta_in_progress() was unresolved.  Simply special-case the
GL_MULTISAMPLE case in the meta code.  There might be other special
cases in the future given all the differences between legacy GL,
core GL, GLES, etc.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=54234
and https://bugs.freedesktop.org/show_bug.cgi?id=54239

v2 (Paul Berry <stereotype441@gmail.com>): keep _meta_in_progress
function, since it's needed by the i965 driver, but don't call it from
core mesa.

Signed-off-by: Brian Paul <brianp@vmware.com>