portico: Drop font-weight for links from landing-page.scss.
portico: Drop font-weight for links from landing-page.scss.

This commit removes "font-weight: 500;" from landing-page.scss so as
to fix a bug on landing pages that used the `markdown` class to
format content. The bug was caused by "a:hover" from landing-page.scss
overriding the font-weight (600) on links as set by the markdown
class, this caused the text to seem jumpy when one hovered over links.

Note from tabbott: The original code was added in
d7f5f31f6a9bd43afeb0f50814e089af0f4eeb4b, which doesn't explain it's
purpose, but it predates the more complete "markdown" CSS, was part of
an early prototype that had unfortunate hover behavior more generally,
and makes sense to remove.

Fixes: #14387.

timabbott/zulip,punchagan/zulip,andersk/zulip,brainwane/zulip,kou/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,andersk/zulip,zulip/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,brainwane/zulip,synicalsyntax/zulip,showell/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,rht/zulip,hackerkid/zulip,shubhamdhama/zulip,timabbott/zulip,hackerkid/zulip,showell/zulip,synicalsyntax/zulip,rht/zulip,shubhamdhama/zulip,synicalsyntax/zulip,andersk/zulip,andersk/zulip,andersk/zulip,kou/zulip,showell/zulip,timabbott/zulip,punchagan/zulip,synicalsyntax/zulip,eeshangarg/zulip,brainwane/zulip,shubhamdhama/zulip,timabbott/zulip,andersk/zulip,synicalsyntax/zulip,hackerkid/zulip,eeshangarg/zulip,shubhamdhama/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,synicalsyntax/zulip,punchagan/zulip,brainwane/zulip,kou/zulip,hackerkid/zulip,showell/zulip,punchagan/zulip,timabbott/zulip,shubhamdhama/zulip,showell/zulip,punchagan/zulip,showell/zulip,zulip/zulip,brainwane/zulip,zulip/zulip,showell/zulip,shubhamdhama/zulip,synicalsyntax/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,brainwane/zulip,shubhamdhama/zulip,timabbott/zulip,kou/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,rht/zulip,kou/zulip,zulip/zulip,rht/zulip